Syd OS: wiki becomes autonomous infrastructure

- wikiBuilder.ts: headless agentic builds via runLLMStream (no chat/SSE) as
  the project owner. Debounced auto-build on document upload (bulk uploads
  collapse into one run, default 2 min after last change; WIKI_BUILD_DEBOUNCE_MS)
  and on document deletion. One build per project; concurrent requests
  coalesce. Model: WIKI_BUILD_MODEL (default claude-sonnet-4-6).
- Routes: POST /projects/:id/wiki/rebuild ({fresh} wipes pages and rebuilds
  from current documents only) + GET /projects/:id/wiki/status.
- Wiki tab: 'Rebuild from scratch' button (confirm), live 'building...' banner
  with status polling, auto-refresh of the page list when a build finishes;
  empty-state copy reflects automatic builds.
- Removed wikiIngest.ts (per-doc haiku summaries) - superseded by full
  debounced builds. Chat tools (read_wiki/upsert_wiki_page) remain for
  corrections, but the wiki no longer depends on the assistant.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>