feat(homecore iter 3): DELETE /api/states/<id> + confirm modal in UI

CRUD increment 3/6. Full delete path lands end-to-end.

Backend (homecore-api):
  rest.rs +18 LOC — new `delete_state` handler. Idempotent (matches HA's
    removal semantics): returns 204 No Content whether the entity existed
    or not. 4xx only for malformed entity_id or auth failure.
  app.rs +6 LOC — adds `.delete(rest::delete_state)` to the
    /api/states/:entity_id route alongside existing GET + POST.

Backend curl smoke:
  POST /api/states/sensor.test_delete         201
  DELETE /api/states/sensor.test_delete       204
  GET /api/states/sensor.test_delete          404

Frontend:
  components/StateCard.ts +25 LOC — small `×` delete button in the
    card's top-right corner. opacity 0 by default, fades in on hover
    or keyboard focus. dispatches `hc-state-card-delete` (NOT
    `hc-state-card-click`) with stopPropagation so the card's own
    click-to-edit handler doesn't also fire.

  pages/Dashboard.ts +45 LOC — deletingState (StateView | null), a
    confirm modal that names the entity_id in the body, Cancel /
    Delete buttons in the footer (Delete styled in muted red),
    `_confirmDelete()` dispatches DELETE with bearer, toast on
    success, grid refresh.

Browser-verified end-to-end on real homecore-server :8123:
  - Hover card → × button visible
  - Click × → DELETE confirm modal (NOT edit modal — stopPropagation works)
  - Modal names entity_id in code block
  - Cancel: entity preserved, modal closes
  - Delete: backend GET-after-DELETE returns 404, grid card vanishes,
    toast "Deleted sensor.delete_target"
  - 0 unexpected console errors (1 expected 404 from verification fetch)

Co-Authored-By: claude-flow <ruv@ruv.net>

frontend/src/components/StateCard.ts

@@ -38,8 +38,27 @@ export class StateCard extends LitElement {
       border-color: hsl(185 80% 50% / 0.4);
     }
 
-    .card { cursor: pointer; }
+    .card { cursor: pointer; position: relative; }
     .card:focus-visible { outline: 2px solid var(--hc-primary, #19d4e5); outline-offset: 2px; }
+    button.delete {
+      position: absolute;
+      top: 0.5rem; right: 0.5rem;
+      width: 24px; height: 24px;
+      border: none;
+      border-radius: 4px;
+      background: transparent;
+      color: var(--hc-text-muted, #7b899d);
+      cursor: pointer;
+      font-size: 16px;
+      line-height: 1;
+      padding: 0;
+      opacity: 0;
+      transition: opacity 150ms, background 150ms, color 150ms;
+    }
+    .card:hover button.delete,
+    .card:focus-within button.delete { opacity: 1; }
+    button.delete:hover { background: hsl(0 50% 30%); color: hsl(0 80% 88%); }
+    button.delete:focus-visible { opacity: 1; outline: 2px solid hsl(0 60% 55%); }
 
     .header {
       display: flex;
@@ -121,6 +140,11 @@ export class StateCard extends LitElement {
            @click=${this._onClick}
            @keydown=${(e: KeyboardEvent) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); this._onClick(); } }}
            aria-label="Edit ${entity_id}">
+        <button class="delete" type="button"
+                @click=${this._onDelete}
+                @keydown=${(e: KeyboardEvent) => { e.stopPropagation(); }}
+                aria-label="Delete ${entity_id}"
+                title="Delete ${entity_id}">×</button>
         <div class="header">
           ${this.iconSvg
             ? html`<div class="icon-wrap" .innerHTML=${this.iconSvg}></div>`
@@ -141,6 +165,15 @@ export class StateCard extends LitElement {
       detail: { state: this.state }, bubbles: true, composed: true,
     }));
   }
+
+  private _onDelete(e: Event) {
+    // Stop propagation so the parent card's click handler (which would
+    // open the edit modal) doesn't also fire.
+    e.stopPropagation();
+    this.dispatchEvent(new CustomEvent('hc-state-card-delete', {
+      detail: { state: this.state }, bubbles: true, composed: true,
+    }));
+  }
 }
 
 declare global {

frontend/src/pages/Dashboard.ts

@@ -103,6 +103,7 @@ export class Dashboard extends LitElement {
     @state() private modalOpen = false;
     @state() private submitToast: string | null = null;
     @state() private editingState: StateView | null = null;  // null = create mode
+    @state() private deletingState: StateView | null = null; // null = no confirm
 
     @query('hc-entity-form') private _form?: EntityForm;
 
@@ -146,6 +147,29 @@ export class Dashboard extends LitElement {
         this.modalOpen = true;
     }
 
+    private _openDeleteConfirm(e: CustomEvent<{ state: StateView }>) {
+        this.deletingState = e.detail.state;
+    }
+
+    private async _confirmDelete() {
+        const target = this.deletingState;
+        if (!target) return;
+        try {
+            const resp = await fetch(`/api/states/${encodeURIComponent(target.entity_id)}`, {
+                method: 'DELETE',
+                headers: { 'Authorization': `Bearer ${resolveToken()}` },
+            });
+            if (!resp.ok) throw new Error(`HTTP ${resp.status}: ${await resp.text()}`);
+            this.deletingState = null;
+            this.submitToast = `Deleted ${target.entity_id}`;
+            window.setTimeout(() => (this.submitToast = null), 3000);
+            await this.refresh();
+        } catch (err) {
+            this.error = err instanceof Error ? err.message : String(err);
+            this.deletingState = null;
+        }
+    }
+
     private async _onSubmit(e: CustomEvent<{ entity_id: string; state: string; attributes: Record<string, unknown> }>) {
         const { entity_id, state, attributes } = e.detail;
         const wasEditing = this.editingState !== null;
@@ -200,12 +224,31 @@ export class Dashboard extends LitElement {
                       <code>--no-seed-entities</code>.
                   </div>`
                 : html`<div class="grid"
-                              @hc-state-card-click=${(e: Event) => this._openEdit(e as CustomEvent)}>
+                              @hc-state-card-click=${(e: Event) => this._openEdit(e as CustomEvent)}
+                              @hc-state-card-delete=${(e: Event) => this._openDeleteConfirm(e as CustomEvent)}>
                       ${this.states.map(
                           (s) => html`<hc-state-card .state=${s}></hc-state-card>`
                       )}
                   </div>`}
 
+            <hc-modal .open=${this.deletingState !== null}
+                      heading="Delete entity"
+                      @hc-modal-close=${() => (this.deletingState = null)}>
+                <p style="margin:0 0 12px 0; line-height:1.5;">
+                    Permanently remove
+                    <code style="background:hsl(220 25% 14%); padding:2px 6px; border-radius:4px;">${this.deletingState?.entity_id ?? ''}</code>
+                    from the state machine?
+                    <br>
+                    <span style="color:var(--hc-text-muted,#7b899d); font-size:12px;">
+                        This is immediate. To restore, re-create the entity via "+ Add entity".
+                    </span>
+                </p>
+                <button slot="footer" class="btn" @click=${() => (this.deletingState = null)}>Cancel</button>
+                <button slot="footer" class="btn"
+                        style="background:hsl(0 50% 25%); border-color:hsl(0 50% 35%); color:hsl(0 60% 88%);"
+                        @click=${this._confirmDelete}>Delete</button>
+            </hc-modal>
+
             <hc-modal .open=${this.modalOpen}
                       heading=${this.editingState ? `Edit ${this.editingState.entity_id}` : 'Add entity'}
                       @hc-modal-close=${() => { this.modalOpen = false; this.editingState = null; }}>

v2/crates/homecore-api/src/app.rs

@@ -28,7 +28,12 @@ pub fn router(state: SharedState) -> Router {
         .route("/api/", get(rest::api_root))
         .route("/api/config", get(rest::get_config))
         .route("/api/states", get(rest::get_states))
-        .route("/api/states/:entity_id", get(rest::get_state).post(rest::set_state))
+        .route(
+            "/api/states/:entity_id",
+            get(rest::get_state)
+                .post(rest::set_state)
+                .delete(rest::delete_state),
+        )
         .route("/api/services", get(rest::get_services))
         .route("/api/services/:domain/:service", post(rest::call_service))
         .route("/api/websocket", get(ws::websocket_handler))

v2/crates/homecore-api/src/rest.rs

@@ -92,6 +92,21 @@ pub struct SetStateRequest {
     pub attributes: serde_json::Value,
 }
 
+/// DELETE /api/states/:entity_id — remove an entity from the state
+/// machine. Idempotent: returns 204 whether or not the entity existed,
+/// matching HA's removal semantics. 4xx only for malformed entity_id or
+/// auth failure.
+pub async fn delete_state(
+    headers: HeaderMap,
+    State(s): State<SharedState>,
+    Path(entity_id): Path<String>,
+) -> ApiResult<StatusCode> {
+    let _ = BearerAuth::from_headers(&headers, s.tokens()).await?;
+    let id = EntityId::parse(entity_id).map_err(|e| ApiError::BadRequest(e.to_string()))?;
+    s.homecore().states().remove(&id);
+    Ok(StatusCode::NO_CONTENT)
+}
+
 pub async fn set_state(
     headers: HeaderMap,
     State(s): State<SharedState>,