fix(wasm-edge): gate ghost_hunter bin behind standalone-bin feature

The standalone ghost_hunter binary defines its own on_init/on_frame/on_timer
WASM3 entry-points; the lib also exports those when default-pipeline is on.
A vanilla `cargo build -p wifi-densepose-wasm-edge --target wasm32-unknown-unknown
--release` would build both, producing a "Linking globals named 'on_frame':
symbol multiply defined!" error.

Fix: declare an explicit `[[bin]] required-features = ["standalone-bin"]`
gate so the bin only builds when the user opts in with
`--no-default-features --features standalone-bin`. The default feature
set continues to produce the combined-pipeline lib (15 KB wasm32).

Validation:
- cargo build -p wifi-densepose-wasm-edge --target wasm32-unknown-unknown
  --release  → 15 KB wifi_densepose_wasm_edge.wasm (default-pipeline lib)
- cargo build -p wifi-densepose-wasm-edge --bin ghost_hunter
  --target wasm32-unknown-unknown --release
  --no-default-features --features standalone-bin
  → 5.8 KB ghost_hunter.wasm (standalone module)
- cd v2/crates/wifi-densepose-wasm-edge && cargo test --features std
  --no-default-features  → 75/75 tests pass

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

v2/crates/wifi-densepose-wasm-edge/Cargo.toml

@@ -25,6 +25,18 @@ std = ["sha2/std"]
 # Include the default combined pipeline (gesture+coherence+adversarial) entry points.
 # Disable this when building standalone module binaries (ghost_hunter, etc.)
 default-pipeline = []
+# Build the standalone-bin Ghost Hunter target. Required because that binary
+# defines its own on_init / on_frame / on_timer entry points which would
+# collide with the lib's `default-pipeline` exports. Build with:
+#   cargo build -p wifi-densepose-wasm-edge --bin ghost_hunter \
+#     --target wasm32-unknown-unknown --release \
+#     --no-default-features --features standalone-bin
+standalone-bin = []
+
+[[bin]]
+name = "ghost_hunter"
+path = "src/bin/ghost_hunter.rs"
+required-features = ["standalone-bin"]
 
 [profile.release]
 opt-level = "s"        # Optimize for size