fix(mcp): refresh complete catalogs and discover active tools

[MelodyVAR]

MCP startup registered only the first catalog page, and find_tools searched a captured built-in list. Collect complete catalogs, refresh filtered additions/updates/removals in one extension-owned batch, and search the active session catalog with callable parameter schemas.

Preserve input schemas and bind output validation/task policy to each captured tool definition, avoiding SDK 1.27.1's mutable per-page metadata cache. Failed refreshes retain the last good catalog; shutdown and one-shot handshake cancellation close outstanding work. The SDK version is unchanged. Related to the closed #154 pagination proposal.

Validation:

• Real local HTTP/SSE MCP and session-registry regressions passed, including pagination, schema changes during pending calls, overlays, shutdown and stalled initialized handshakes.
• npm run check
• pnpm run build:offline
• ./test.sh with isolated credentials