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/src/api/chapters.rs

@@ -137,6 +137,7 @@ async fn create(
     )
     .await?;
 
+    let mut page_ids: Vec<Uuid> = Vec::with_capacity(pages.len());
     for (idx, page) in pages.iter().enumerate() {
         let page_number = (idx + 1) as i32;
         let nnnn = format!("{:04}", page_number);
@@ -145,7 +146,9 @@ async fn create(
             manga_id, chapter.id, nnnn, page.ext
         );
         state.storage.put(&key, &page.bytes).await?;
-        repo::page::create(&mut *tx, chapter.id, page_number, &key, page.mime).await?;
+        let created =
+            repo::page::create(&mut *tx, chapter.id, page_number, &key, page.mime).await?;
+        page_ids.push(created.id);
     }
 
     let page_count = pages.len() as i32;
@@ -154,6 +157,20 @@ async fn create(
 
     tx.commit().await?;
 
+    // Enqueue AI content-analysis for each new page. Done after commit so a
+    // rolled-back upload never leaves jobs pointing at nonexistent pages; a
+    // failed enqueue is logged but doesn't fail the upload (the admin
+    // re-enqueue endpoint can backfill).
+    if state.analysis_enabled {
+        for page_id in page_ids {
+            if let Err(e) =
+                repo::page_analysis::enqueue_for_page(&state.db, page_id, false).await
+            {
+                tracing::warn!(%page_id, error = %e, "failed to enqueue page analysis");
+            }
+        }
+    }
+
     Ok((StatusCode::CREATED, Json(chapter)))
 }