fix(import): persist object_key + metadata; add nav + logout session cleanup

- Import task: persist object_key, author, cover_url, genres, summary,
  book_status in PocketBase so the runner can fetch the file and write
  book metadata on completion
- Runner poll mode: pass task.ObjectKey instead of empty string
- Runner: write BookMeta + UpsertBook in Meilisearch after chapter ingest
  so imported books appear in catalogue and search
- Import UI: add author, cover URL, genres, summary, status fields; add
  AI tasks panel (chapter names, description, image gen, tagline) after
  import completes; add AI tasks button on each done task in the list
- Admin nav: add Notifications entry to sidebar (all 5 locales)
- Logout: delete user_sessions row on sign-out so sessions don't
  accumulate as phantoms after each login/logout cycle

backend/internal/runner/runner.go

@@ -432,9 +432,7 @@ importLoop:
 			defer wg.Done()
 			defer func() { <-importSem }()
 			defer r.tasksRunning.Add(-1)
-			// Import tasks need object key - we'll need to fetch it from the task record
-			// For now, assume it's stored in a field or we need to add it
-			r.runImportTask(ctx, t, "")
+			r.runImportTask(ctx, t, t.ObjectKey)
 		}(task)
 	}
 }
@@ -753,6 +751,31 @@ func (r *Runner) runImportTask(ctx context.Context, task domain.ImportTask, obje
 		return
 	}
 
+	// Write book metadata so the book appears in PocketBase catalogue.
+	if r.deps.BookWriter != nil {
+		meta := domain.BookMeta{
+			Slug:          task.Slug,
+			Title:         task.Title,
+			Author:        task.Author,
+			Cover:         task.CoverURL,
+			Status:        task.BookStatus,
+			Genres:        task.Genres,
+			Summary:       task.Summary,
+			TotalChapters: len(chapters),
+		}
+		if meta.Status == "" {
+			meta.Status = "completed"
+		}
+		if err := r.deps.BookWriter.WriteMetadata(ctx, meta); err != nil {
+			log.Warn("runner: import task WriteMetadata failed (non-fatal)", "err", err)
+		} else {
+			// Index in Meilisearch so the book is searchable.
+			if err := r.deps.SearchIndex.UpsertBook(ctx, meta); err != nil {
+				log.Warn("runner: import task meilisearch upsert failed (non-fatal)", "err", err)
+			}
+		}
+	}
+
 	r.tasksCompleted.Add(1)
 	span.SetStatus(codes.Ok, "")
 	result := domain.ImportResult{