feat(analysis): enqueue page-analysis on upload/crawl + admin backfill endpoints

Wires the analyze_page job kind into the page-create paths and adds admin
controls, all gated on a new ANALYSIS_ENABLED flag (AppState.analysis_enabled,
config::AnalysisConfig):

- Chapter upload (api::chapters) enqueues one analyze_page job per page
  after the tx commits (best-effort; failures logged, never fatal).
- Crawler content sync (persist_pages → RETURNING id) enqueues per
  persisted page when the daemon dispatcher's analysis_enabled flag is set;
  threaded through sync_chapter_content (CLI/resync pass false).
- repo::page_analysis::enqueue_all_pages: bulk backfill via INSERT..SELECT,
  skipping done pages (only_unanalyzed) and existing pending jobs.
- New admin endpoints (RequireAdmin, 503 when disabled, audited):
  POST /admin/analysis/reenqueue and POST /admin/pages/:id/analyze (force).

Tests: upload enqueues N jobs / no-op when disabled; crawler persist_pages
enqueue gate; admin reenqueue (backfill, idempotent, only-unanalyzed, 503,
non-admin 403) and force-analyze (force flag, 404).

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

backend/Cargo.lock

@@ -1470,7 +1470,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.65.0"
+version = "0.66.0"
 dependencies = [
  "anyhow",
  "argon2",