feat(analysis): admin UI — reader context-menu action + dashboard section

Surfaces the scoped re-enqueue and per-page force-analyze in the UI:

- api/admin: reenqueueAnalysis({onlyUnanalyzed, mangaId, chapterId}) and
  analyzePage(pageId).
- Reader PageContextMenu gains an admin-only "Queue for analysis" item
  (canAnalyze/onAnalyzePage/analyzeState props) wired to the force-analyze
  endpoint with inline busy/done/error feedback; reset per page.
- New /admin/analysis dashboard section + nav tab: scope selector
  (whole library / one manga / one chapter), id input, and an
  "include already-analyzed" toggle (default off), with busy/notice/error.

Tests: vitest for the two clients; Playwright for the context-menu action
(admin vs non-admin) and the admin section (scope + include toggle +
validation). svelte-check + build clean; 262 vitest, 10 new e2e green.

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

backend/Cargo.lock

@@ -1517,7 +1517,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.72.0"
+version = "0.73.0"
 dependencies = [
  "anyhow",
  "argon2",