feat: add admin UI dashboard with static serving

- Add admin-ui/index.html: web-based dashboard for monitoring hub
- Add admin-ui/README.md: setup instructions for OBSERVE_SECRET connection
- Configure nginx to serve admin-ui/ statically at /admin-ui/ location
- No separate server process needed, UI uses WebSocket to connect
- OBSERVE_SECRET provides auth layer, no nginx auth required

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

admin-ui/README.md

@@ -0,0 +1,61 @@
+# Admin UI
+
+A web-based dashboard for monitoring the MCP Hub in real-time.
+
+## Setup
+
+### 1. Get Your OBSERVE_SECRET
+
+The `OBSERVE_SECRET` is stored in `/workspace/.env` on the hub server. Extract it:
+
+```bash
+# On the hub server:
+grep OBSERVE_SECRET /workspace/.env
+```
+
+Copy the secret value (it's a long hex string).
+
+### 2. Open the UI
+
+#### Option A: Via https (production)
+```
+https://mcp.arik.work/admin-ui/
+```
+
+#### Option B: Local development with file:// (offline)
+```bash
+# Simply open the file in your browser:
+file:///workspace/admin-ui/index.html
+```
+
+#### Option C: Local development with HTTP server
+```bash
+cd /workspace/admin-ui
+python3 -m http.server 8080
+# Then open http://localhost:8080
+```
+
+### 3. Connect to the Hub
+
+In the UI, enter:
+- **Hub URL**: `wss://mcp.arik.work/ws/observe` (production) or `ws://localhost:3000/ws/observe` (local dev)
+- **OBSERVE_SECRET**: Paste the value from step 1
+
+The status light will turn **green** when connected.
+
+### 4. Monitor
+
+- **Backends**: View connected MCP backends
+- **Logs**: Real-time event stream from the hub
+- **Status**: Connection indicator at the top
+
+## Adding More Backends
+
+To connect additional backends to the hub, edit `/workspace/.env` on the hub server:
+
+```env
+OBSERVE_SECRET=...
+# Add new backends via environment config or the hub's register endpoint
+```
+
+Then restart the hub to pick up new backends.