feat(analysis): worker daemon + real dispatcher + app wiring

The background analysis worker that drains analyze_page jobs:

- analysis::daemon: a lean sibling of the crawler daemon — leases only
  KIND_ANALYZE_PAGE, skip-if-done-unless-force, lease heartbeat, panic +
  timeout isolation, ack done/failed, and a failed page_analysis row on
  terminal (dead-lettered) failure. AnalyzeDispatcher trait seam.
- RealAnalyzeDispatcher: load page → storage.get → VisionClient.analyze →
  persist_analysis (skips a deleted page; caps image bytes).
- app::build spawns the daemon (own plain reqwest client) when
  ANALYSIS_ENABLED; AppHandle/main shut it down alongside the crawler.
- repo::page::find_by_id.

Tests: dispatch+ack-done, skip-when-done, force re-dispatch, terminal
failure writes failed row, panic isolation, ignores non-analyze jobs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/analysis/mod.rs

@@ -7,5 +7,6 @@
 //! * [`vision`] — the HTTP client: downscale → request → parse → sanitize.
 //! * [`daemon`] — the job-leasing worker loop (added in the worker phase).
 
+pub mod daemon;
 pub mod prompt;
 pub mod vision;