feat(ai): serveur MCP Streamable HTTP + confirmations two-step (#79 phase E)

backend/main.py

@@ -800,6 +800,7 @@ class SSESafeGZipMiddleware(GZipMiddleware):
         "/api/admin/stream",
         "/api/ai/bookslm/chat",
         "/api/ai/bookslm/agent",
+        "/mcp",
     )
 
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
@@ -882,6 +883,14 @@ try:
 except ImportError as e:
     logger.warning(f"Could not load plugins router: {e}")
 
+# MCP server (Streamable HTTP) for external clients (#79 phase E)
+try:
+    from backend.mcp.server import McpMount, mcp_app
+    app.router.routes.append(McpMount(mcp_app))
+    logger.info("MCP server mounted at /mcp")
+except Exception as e:  # pragma: no cover - optional dependency
+    logger.warning(f"Could not mount MCP server: {e}")
+
 # Resolve frontend path relative to this file
 FRONTEND_DIR = Path(__file__).resolve().parent.parent / "frontend"