[Enhancement] Settings UI for MCP configuration

[Wan-ZL]

Description

Add a user-friendly Settings UI for configuring MCP (Model Context Protocol) servers. Currently, MCP can only be configured via API or CLI.

Current State

MCP functionality is fully working (verified in #51), but lacks a UI. Users must use:

# Enable MCP via API
curl -X PUT http://localhost:8080/api/settings -d '{"mcp_enabled": true}'

# Add server via API
curl -X POST http://localhost:8080/api/mcp/servers \
  -d '{
    "name": "filesystem",
    "transport": "stdio",
    "command": ["npx", "-y", "@modelcontextprotocol/server-filesystem", "/path"],
    "env": {}
  }'

Desired State

Add MCP configuration section to Settings page (settings.html):

1. Enable/Disable MCP: Toggle switch for mcp_enabled
2. MCP Servers List: Display configured servers with status
   • Server name
   • Transport type (stdio/sse)
   • Connection status (connected/disconnected)
   • Tool count
3. Add Server Form:
   • Name (text input)
   • Transport type (dropdown: stdio, sse)
   • Command (array input for stdio)
   • URL (text input for sse)
   • Environment variables (key-value pairs)
4. Actions: Connect, Disconnect, Remove server buttons

Acceptance Criteria

• Settings page has "MCP Configuration" section
• Toggle to enable/disable MCP
• List of configured MCP servers with status
• "Add Server" button opens form modal
• Form validates transport-specific requirements (command for stdio, URL for sse)
• Connect/Disconnect buttons work and update status in real-time
• Remove server button with confirmation dialog
• All changes persist to database
• UI updates when MCP manager connects/disconnects servers

UI Mockup

┌─────────────────────────────────────┐
│ MCP Configuration                   │
├─────────────────────────────────────┤
│ [x] Enable MCP Support              │
│                                     │
│ Configured Servers:                 │
│ ┌─────────────────────────────────┐ │
│ │ filesystem (stdio)              │ │
│ │ Status: Connected | Tools: 5    │ │
│ │ [Disconnect] [Remove]           │ │
│ └─────────────────────────────────┘ │
│                                     │
│ [+ Add MCP Server]                  │
└─────────────────────────────────────┘

Technical Notes

• Reuse existing settings UI patterns from static/settings.html
• API endpoints already exist:
  • GET /api/mcp/servers
  • POST /api/mcp/servers
  • DELETE /api/mcp/servers/{name}
  • POST /api/mcp/servers/{name}/connect
  • POST /api/mcp/servers/{name}/disconnect
• No backend changes needed, pure frontend work

Priority Rationale

LOW: MCP is fully functional without UI. This is a UX enhancement for users who prefer GUI over CLI/API.

Related

• [Feature] MCP (Model Context Protocol) support for tool integration #51 (MCP implementation - verified and complete)
• assistant/docs/MCP_SETUP.md (user guide with CLI examples)