fix(GRO-1544): register health endpoint at /api/health on app

Corrected: use app.get("/api/health", ...) instead of api.get("/health", ...).
api is not declared until ~130 lines later — const has no hoisting,
causing TDZ ReferenceError at startup.

Health endpoint registered on app at full path /api/health, before
any auth middleware, so it's reachable from outside the cluster.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/index.ts

@@ -58,8 +58,8 @@ app.use(
   })
 );
 
-// Health check — registered on api before auth middleware so it is reachable at /api/health
-api.get("/health", (c) => c.json({ status: "ok" }));
+// Health check — no auth required, registered on app at full path before auth middleware
+app.get("/api/health", (c) => c.json({ status: "ok" }));
 
 // Public booking routes — no auth required, must be registered before auth middleware
 app.route("/api/book", bookRouter);