Replace SSE with REST API for web UI

[aniongithub]

Summary

Replace MCP-over-SSE with a plain REST API for the web UI. Agents use stdio, browsers use REST.

What changed

Server (cmd/mind-map/main.go)

• Removed mcp.NewSSEHandler and /mcp endpoint
• Added REST endpoints:
  • GET /api/context -- wiki overview
  • GET /api/pages?prefix=... -- list pages
  • GET /api/pages/{path} -- get page
  • POST /api/pages -- create page
  • PUT /api/pages/{path} -- update page
  • DELETE /api/pages/{path} -- delete page
  • GET /api/search?q=... -- full-text search
  • GET /api/backlinks/{path} -- backlinks
• go-sdk/mcp import now only used for stdio transport

Web UI (webui/src/mcp.ts)

• Rewrote from SSE/JSON-RPC client (EventSource, session handshake, pending request map, reconnect logic) to plain fetch() REST calls
• Dropped from 154 lines to 85 lines

Architecture

Transport	Users	Protocol
stdio	Agents (Copilot, Claude, etc.)	MCP JSON-RPC
HTTP	Web UI (browser)	REST

Why

• SSE required multi-step handshake (EventSource -> session endpoint -> JSON-RPC POST) that smaller models struggled with
• stdio is more reliable for agent use and is natively supported by all MCP clients
• REST is simpler for the web UI -- no reconnection logic, no session state, no protocol negotiation
• Reduced web UI bundle size

Testing

• go vet clean
• All Go tests pass
• WebUI builds successfully