feat(homecore-ui iter 2): Edit Entity modal + shadow-DOM focus delegation

CRUD increment 2/6 — clicking any state card on the Dashboard opens
the Add Entity modal in EDIT mode: pre-populated, entity_id locked,
"Save" primary button, idempotent POST to /api/states/<id> (backend
returns 200 if existed, 201 if created — same handler).

frontend/src/components/StateCard.ts:
  - card div is now role="button" tabindex=0, dispatches
    `hc-state-card-click` on click + Enter/Space keydown
  - aria-label="Edit <entity_id>" for screen readers
  - shadowRootOptions delegatesFocus=true so the outer Tab sequence
    can reach the inner focusable div (caught by browser agent —
    without this Tab couldn't pierce the shadow root)

frontend/src/pages/Dashboard.ts:
  - new state: editingState (null = create, StateView = edit)
  - _openEdit() catches `hc-state-card-click` from the grid container
  - modal heading switches: "Add entity" ↔ "Edit <entity_id>"
  - primary button text switches: "Create" ↔ "Save"
  - EntityForm receives .editing=true so entity_id input is disabled
  - submit toast reads "Updated" or "Created" depending on mode

Browser-verified end-to-end (real homecore-server :8123, 12 entities):
  - Click `light.kitchen_ceiling` → modal opens with all 4 attributes
    (brightness=230, color_temp_kelvin=4000, friendly_name,
    supported_color_modes) pre-populated
  - Change state to "off", click Save → toast "Updated
    light.kitchen_ceiling = off", grid card reflects new state
  - Backend curl confirms /api/states/light.kitchen_ceiling.state = "off"
  - Enter key on focused card opens the modal too
  - 0 console errors

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

frontend/src/components/StateCard.ts

@@ -9,6 +9,12 @@ import type { StateView } from '../api/types.js';
 
 @customElement('hc-state-card')
 export class StateCard extends LitElement {
+  // `delegatesFocus` lets Tab key traversal from the light DOM reach the
+  // role="button" element inside this card's shadow root. Without it the
+  // user can only activate the card via mouse click or by JS-focusing the
+  // inner div; with it, the natural tab sequence flows through every card.
+  static shadowRootOptions = { ...LitElement.shadowRootOptions, delegatesFocus: true };
+
   @property({ type: Object }) state!: StateView;
   /** Optional: icon SVG string (use `iconSvg()` from lucide.ts) */
   @property({ type: String }) iconSvg?: string;
@@ -32,6 +38,9 @@ export class StateCard extends LitElement {
       border-color: hsl(185 80% 50% / 0.4);
     }
 
+    .card { cursor: pointer; }
+    .card:focus-visible { outline: 2px solid var(--hc-primary, #19d4e5); outline-offset: 2px; }
+
     .header {
       display: flex;
       align-items: flex-start;
@@ -108,7 +117,10 @@ export class StateCard extends LitElement {
     const badge = this.badgeClass(state);
 
     return html`
-      <div class="card" part="card">
+      <div class="card" part="card" role="button" tabindex="0"
+           @click=${this._onClick}
+           @keydown=${(e: KeyboardEvent) => { if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); this._onClick(); } }}
+           aria-label="Edit ${entity_id}">
         <div class="header">
           ${this.iconSvg
             ? html`<div class="icon-wrap" .innerHTML=${this.iconSvg}></div>`
@@ -123,6 +135,12 @@ export class StateCard extends LitElement {
       </div>
     `;
   }
+
+  private _onClick() {
+    this.dispatchEvent(new CustomEvent('hc-state-card-click', {
+      detail: { state: this.state }, bubbles: true, composed: true,
+    }));
+  }
 }
 
 declare global {

frontend/src/pages/Dashboard.ts

@@ -102,6 +102,7 @@ export class Dashboard extends LitElement {
     @state() private loading = true;
     @state() private modalOpen = false;
     @state() private submitToast: string | null = null;
+    @state() private editingState: StateView | null = null;  // null = create mode
 
     @query('hc-entity-form') private _form?: EntityForm;
 
@@ -135,8 +136,19 @@ export class Dashboard extends LitElement {
         }
     }
 
+    private _openCreate() {
+        this.editingState = null;
+        this.modalOpen = true;
+    }
+
+    private _openEdit(e: CustomEvent<{ state: StateView }>) {
+        this.editingState = e.detail.state;
+        this.modalOpen = true;
+    }
+
     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;
         try {
             const resp = await fetch(`/api/states/${encodeURIComponent(entity_id)}`, {
                 method: 'POST',
@@ -148,11 +160,11 @@ export class Dashboard extends LitElement {
             });
             if (!resp.ok) throw new Error(`HTTP ${resp.status}: ${await resp.text()}`);
             this.modalOpen = false;
-            this.submitToast = `Created ${entity_id} = ${state}`;
+            this.editingState = null;
+            this.submitToast = `${wasEditing ? 'Updated' : 'Created'} ${entity_id} = ${state}`;
             window.setTimeout(() => (this.submitToast = null), 3000);
             await this.refresh();
         } catch (err) {
-            // Form-level error stays in the form; surface at top too for visibility.
             this.error = err instanceof Error ? err.message : String(err);
         }
     }
@@ -173,7 +185,7 @@ export class Dashboard extends LitElement {
             ${this.submitToast ? html`<div class="toast">${this.submitToast}</div>` : ''}
             <div class="toolbar">
                 <span class="grow"></span>
-                <button class="add" @click=${() => (this.modalOpen = true)}>+ Add entity</button>
+                <button class="add" @click=${this._openCreate}>+ Add entity</button>
             </div>
             <div class="meta">
                 <span><strong>${loc}</strong></span>
@@ -187,19 +199,25 @@ export class Dashboard extends LitElement {
                       or boot <code>homecore-server</code> without
                       <code>--no-seed-entities</code>.
                   </div>`
-                : html`<div class="grid">
+                : html`<div class="grid"
+                              @hc-state-card-click=${(e: Event) => this._openEdit(e as CustomEvent)}>
                       ${this.states.map(
                           (s) => html`<hc-state-card .state=${s}></hc-state-card>`
                       )}
                   </div>`}
 
-            <hc-modal .open=${this.modalOpen} heading="Add entity"
-                      @hc-modal-close=${() => (this.modalOpen = false)}>
+            <hc-modal .open=${this.modalOpen}
+                      heading=${this.editingState ? `Edit ${this.editingState.entity_id}` : 'Add entity'}
+                      @hc-modal-close=${() => { this.modalOpen = false; this.editingState = null; }}>
                 <hc-entity-form
+                    .entityId=${this.editingState?.entity_id ?? ''}
+                    .state=${this.editingState?.state ?? ''}
+                    .entityAttrs=${this.editingState?.attributes ?? {}}
+                    .editing=${this.editingState !== null}
                     @hc-entity-submit=${(e: Event) => this._onSubmit(e as CustomEvent)}
-                    @hc-entity-cancel=${() => (this.modalOpen = false)}></hc-entity-form>
+                    @hc-entity-cancel=${() => { this.modalOpen = false; this.editingState = null; }}></hc-entity-form>
                 <button slot="footer" class="btn" @click=${() => this._form?.requestCancel()}>Cancel</button>
-                <button slot="footer" class="btn primary" @click=${() => this._form?.requestSubmit()}>Create</button>
+                <button slot="footer" class="btn primary" @click=${() => this._form?.requestSubmit()}>${this.editingState ? 'Save' : 'Create'}</button>
             </hc-modal>
         `;
     }