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/domain/domain.go

@@ -177,6 +177,12 @@ type ImportTask struct {
 	Title            string     `json:"title"`
 	FileName         string     `json:"file_name"`
 	FileType         string     `json:"file_type"` // "pdf" or "epub"
+	ObjectKey        string     `json:"object_key,omitempty"` // MinIO path to uploaded file
+	Author           string     `json:"author,omitempty"`
+	CoverURL         string     `json:"cover_url,omitempty"`
+	Genres           []string   `json:"genres,omitempty"`
+	Summary          string     `json:"summary,omitempty"`
+	BookStatus       string     `json:"book_status,omitempty"` // "ongoing" | "completed" | "hiatus"
 	WorkerID         string     `json:"worker_id,omitempty"`
 	InitiatorUserID  string     `json:"initiator_user_id,omitempty"` // PocketBase user ID who submitted the import
 	Status           TaskStatus `json:"status"`