feat(instance-proxy): add HTTP proxy for tool instances

Add API proxy endpoint so users can access running tool instances
through the backend API instead of internal Docker network.

Backend:
- Add container_name field to ToolInstance model
- Create /instances/{id}/proxy/{path:path} endpoint with ownership checks
- Proxy HTTP requests to containers via docker network using container names
- Support all HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS)
- Store proxy URL in instance.url instead of localhost
- Add Alembic migration 0007 for container_name column
- Add get_container_name() utility to docker.py

Frontend:
- Update Open button to use full proxy URL (API_BASE_URL + instance.url)

Closes instance-proxy OpenSpec change.

apps/api/src/services/docker.py

@@ -113,6 +113,26 @@ def get_container_id(instance_name: str) -> str | None:
     return None
 
 
+def get_container_name(instance_name: str) -> str | None:
+    """Get the full container name for a compose service.
+
+    Args:
+        instance_name: The service name in compose
+
+    Returns:
+        Container name or None if not found
+    """
+    result = subprocess.run(
+        ["docker", "ps", "--format", "{{.Names}}", "--filter", f"name={instance_name}"],
+        capture_output=True,
+        text=True,
+    )
+
+    if result.returncode == 0 and result.stdout.strip():
+        return result.stdout.strip().split("\n")[0]
+    return None
+
+
 def get_container_status(container_id: str) -> str:
     """Get the status of a Docker container.