Add MCP routes for Context7 and Playwright

[frits-v]

Summary

Add explicit MCP routing for Context7 (documentation lookups) and Playwright (local browser automation) so they auto-allow instead of hitting the FR-MR-7 unknown MCP catch-all.

Prefixes

Server	Prefix	Rationale
Context7	mcp__context7__	Read-only doc lookups
Context7 (plugin)	mcp__plugin_context7_context7__	Same, plugin-namespaced
Playwright	mcp__playwright__	Local browser automation
Playwright (plugin)	mcp__plugin_playwright_playwright__	Same, plugin-namespaced

All tools from these servers are safe to auto-allow — Context7 only does documentation fetches, Playwright only drives a local browser.

Current state

A local patch exists in src/mcp.rs (applied directly to the installed binary). This issue tracks upstreaming it with proper tests.

Acceptance criteria

• Routes added in src/mcp.rs before the FR-MR-7 catch-all
• Tests for all four prefixes
• Release binary updated