perf(mcp): optimize test performance with parallel connections and reduced retries

- Connect to MCP servers concurrently instead of sequentially
- Reduce retry settings in test mode (IS_TEST=True):
  - 1 attempt instead of 3
  - 100ms retry delay instead of 1s
  - 2s timeout instead of 30-120s

Reduces MCP E2E test time from ~16s to under 1s.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/services/mcp/client_manager.py

@@ -122,16 +122,24 @@ class MCPClientManager:
             )
 
     async def _connect_all_servers(self) -> None:
-        """Connect to all enabled MCP servers."""
+        """Connect to all enabled MCP servers concurrently."""
+        import asyncio
+
         enabled_servers = self._registry.get_enabled_configs()
 
-        for name, config in enabled_servers.items():
+        async def connect_server(name: str, config: "MCPServerConfig") -> None:
             try:
                 await self._pool.get_connection(name, config)
                 logger.info("Connected to MCP server: %s", name)
             except Exception as e:
                 logger.error("Failed to connect to MCP server %s: %s", name, e)
 
+        # Connect to all servers concurrently for faster startup
+        await asyncio.gather(
+            *(connect_server(name, config) for name, config in enabled_servers.items()),
+            return_exceptions=True,
+        )
+
     async def shutdown(self) -> None:
         """
         Shutdown the MCP client manager.