fix(gensui): correct frontend dist path resolution

GENSUI_ROOT (gensui/config.py:14) resolves to /app/gensui — the
Python package directory. app.py used GENSUI_ROOT / "frontend" / "dist"
to locate the built admin UI, but the Docker image places the built
frontend one level up, at /app/frontend/dist (see gensui/Dockerfile:31,
`COPY --from=frontend-builder /app/frontend/dist ./frontend/dist`
under WORKDIR /app).

Effect: frontend_dist.exists() was always False inside the container,
so the `/` route and the SPA catch-all were never registered. Every
request to the root or any client-side route returned FastAPI's
default 404:

  $ curl -s http://127.0.0.1:8787/
  {"detail":"Not Found"}

...despite the built files being present and intact:

  $ docker exec gensui ls /app/frontend/dist/index.html
  /app/frontend/dist/index.html

Fix: try GENSUI_ROOT.parent / "frontend" / "dist" first (matches the
Docker layout), falling back to the original GENSUI_ROOT / "frontend"
/ "dist" if that doesn't exist — preserves behavior for the local
`install.sh` install path, which may lay out files differently.

After fix:
  $ curl -s -o /dev/null -w "%{http_code}" http://127.0.0.1:8787/
  200

Author: wstlima

gensui/app.py

@@ -118,7 +118,9 @@ async def health_check():
         return {"status": "ok", "service": "gensui", "version": "0.1.0"}
 
     # ── Serve Frontend (production) ──────────────────────────
-    frontend_dist = GENSUI_ROOT / "frontend" / "dist"
+    frontend_dist = GENSUI_ROOT.parent / "frontend" / "dist"
+    if not frontend_dist.exists():
+        frontend_dist = GENSUI_ROOT / "frontend" / "dist"
     if frontend_dist.exists():
         # Serve /assets/* static files
         assets_path = frontend_dist / "assets"