feat(analysis): live SSE event stream for the admin dashboard

Broadcasts analysis progress so the dashboard updates live:

- analysis::events: AnalysisEvents broadcaster + AnalysisEvent
  (Enqueued / Started / Completed / Failed), carrying the
  manga/chapter/page breadcrumb.
- The worker daemon resolves each page's breadcrumb (repo::page::locate)
  and publishes Started before dispatch and Completed/Failed after.
- The admin reenqueue publishes Enqueued (scoped by manga/chapter).
- GET /v1/admin/analysis/status/stream — SSE (RequireAdmin) forwarding
  each event as a named `analysis` frame; broadcast lag emits a `lagged`
  frame. AppState carries the always-present events bus.

Tests: worker publishes started+completed (with breadcrumb) and failed;
SSE route is admin-gated (403 non-admin) and returns text/event-stream.

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

backend/tests/api_admin_role.rs

@@ -53,6 +53,7 @@ fn admin_test_router(pool: PgPool) -> (Router, TempDir) {
         crawler: None,
         admin_allowed_origins: Arc::new(Vec::new()),
         analysis_enabled: false,
+        analysis_events: Arc::new(mangalord::analysis::events::AnalysisEvents::new()),
     };
     let app = Router::new()
         .nest("/api/v1", api::routes())