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>

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>,