fix(summarizer): isolate MCP servers and settings in summarizer subprocess

[madorb]

What

The background summarizer (summarizer.ts → buildSummarizerQueryOptions) runs each archived conversation through the Claude Agent SDK with resume + the conversation's cwd. The SDK loads all filesystem settings by default, so every summarization boots the user's entire global MCP server set — one MCP fleet spawned per conversation. MCP servers that open a GUI (e.g. Serena's web dashboard) pop a window per conversation; the rest start and tear down silently, churning CPU/RAM. With a backlog of N conversations, a single SessionStart sync fans out to N × (whole MCP fleet).

Same root mechanism as #83 (resume → full Claude Code session subprocess) and the MCP-config analog of #104 (summarizer inheriting global env).

Change

Two options added to the summarizer's query():

• settingSources: [] — the SDK's documented isolation mode ("Pass [] to disable filesystem settings (SDK isolation mode)"). This is the actual leak: the option is currently omitted, and the SDK docs note that when omitted, all sources are loaded.
• mcpServers: {} — makes the empty server set explicit.

A summarizer needs no tools or MCP servers. This sits alongside the existing persistSession: false isolation (#83).

Testing

• npm run build — clean (tsc + esbuild).
• npm test — 209 passed. One unrelated failure: a beforeEach hook timeout in search-metadata-filters from a cold embedding-model load exceeding the 10s hook limit (not touched by this change; later tests in that same file pass).
• Added 3 assertions to test/summarizer-options.test.ts covering settingSources: [] and mcpServers: {} on both fresh and resumed option builds.

Notes

• Rebuilt dist/ for the changed module (dist/summarizer.js, dist/summarizer.d.ts), per CLAUDE.md.
• Left the unrelated dist/version.* / dist/mcp-server.js version-string drift (committed 1.4.1 vs package.json 1.4.2) untouched to keep this PR focused on the fix.

Fixes #106