Migrate web tools (web_search, web_view, http_request) to navi-web MCP server ...

New MCP server: mcp-servers/navi-web/
- app/search.py    — SearXNG primary, DDG fallback, Brave tertiary
- app/browse.py    — Playwright headless browser page extraction
- app/request.py   — httpx raw HTTP requests
- app/mcp_server.py — FastMCP entry point with stdio transport
- pyproject.toml   — deps: mcp, httpx, ddgs, playwright, pydantic

Changes:
- Added "navi-web" block to mcp_servers.json (stdio transport)
- Removed web_search, web_view, http_request from built-in registry
- Removed them from navi/tools/__init__.py
- Removed them from enabled_tools / subagent_tools in all profiles
- Added "navi-web": ["search", "browse", "request"] to mcp_servers
  in all profiles (developer, secretary, server_admin, tool_developer,
  modeler_3d, discuss)

Tests: 240 passed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>