Add URL-based MCP support

[Code-MonkeyZhang]

Description

mini_agent/tools/mcp_loader.py only recognizes STDIO (command/args). If the config uses the official URL-direct style (many MCPs use this format: Notion, ZhiPu Search...), the loader prints “No command specified” and skips the server.

Steps to Reproduce

Put this in mini_agent/config/mcp.json:

{
  "mcpServers": {
    "Notion": { "url": "https://mcp.notion.com/mcp" }
  }
}

1. Start mini-agent.
2. Logs show No command specified for server: Notion; the MCP is not loaded.

Cleaning up MCP connections...
✅ Cleanup complete

(mini-agent) (base) zhangyufeng@zhangyufengdeMacBook-Air Mini-Agent-Original % mini-agent
✅ LLM retry mechanism enabled (max 3 retries)
✅ Loaded Bash tool
✅ Loaded Bash Output tool
✅ Loaded Bash Kill tool
Loading MCP tools...
Skipping disabled server: minimax_search
Skipping disabled server: memory
INFO:ticktick_mcp.src.config:TickTick client initialized successfully
INFO:ticktick_mcp.src.config:Successfully connected to TickTick API with 6 projects
INFO:ticktick_mcp.src.server:All TickTick MCP tools registered successfully
INFO:mcp.server.lowlevel.server:Processing request of type ListToolsRequest

No command specified for server: Notion

Expected Result

• Loader supports URL-based direct connections (type: http/streamable_http or type: sse) when url is provided.
• Keep compatibility with command/args STDIO mode.

Suggested Improvement

• In mcp_loader.py, add a branch: if url exists, create an HTTP/SSE connection based on type (default http/streamable_http); otherwise fall back to STDIO.