fix: reconcile routing host disablement

[pacphi]

Summary

Fixes #73: excluding a routing host now performs a complete, ownership-safe disable rather than only flipping its config flag.

• prune disabled hosts from persisted routes and escalation ladders
• warn before removing user-pinned routes
• project only explicitly configured routes into AQE, avoiding default-route reintroduction
• prune stale agentic-kit-curated AQE overrides while preserving foreign overrides
• retire only marker-owned Codex MCP bridges; re-enable converges them normally
• document the unified disable semantics

Verification

• pnpm run check
• sandboxed command tests assert the exact owned Codex MCP removal calls

This follows #77 and closes the disable-semantics gap before generalized routing can safely expand.