feat: ML tag suggestions, character/fandom integrity, underscores, modal polish

Consolidated merge of feat/tag-suggestions branch. Original 64-commit history
was lost to git-object corruption in a Nextcloud-synced checkout; this single
commit captures the equivalent diff.

Includes:
- pgvector-backed tag suggestion infra (WD14 + SigLIP centroids, ml-worker
  container, Celery tasks, suggestion service, accept/reject endpoints + modal
  UI with green/red chip buttons)
- Character/fandom integrity: title-case normalization on every write path,
  fandom-id backfill, maintenance task + settings button, migrations g26041901
  + h26041901 to canonicalize legacy rows with case-only duplicate merging
- Tag-underscores + modal polish: WD14 name canonicalization at emit + accept
  + add/bulk-add paths, migration i26041901 for legacy-row rename-or-merge
  across character/fandom/NULL kinds, suggestion-accept refresh parity via
  awaited loadTags, persistent chip tint

app/celery_app.py

@@ -37,7 +37,9 @@ def make_celery(app=None):
             'app.tasks.scan',
             'app.tasks.import_file',
             'app.tasks.thumbnail',
-            'app.tasks.sidecar'
+            'app.tasks.sidecar',
+            'app.tasks.ml',
+            'app.tasks.maintenance',
         ]
     )
 
@@ -69,11 +71,15 @@ def make_celery(app=None):
             'app.tasks.scan.cleanup_old_tasks': {'queue': 'maintenance'},
             'app.tasks.scan.update_system_stats': {'queue': 'maintenance'},
             'app.tasks.scan.update_batch_stats': {'queue': 'maintenance'},
+            'app.tasks.maintenance.sync_character_fandoms': {'queue': 'maintenance'},
 
             # Import tasks - handled by worker (heavy processing)
             'app.tasks.import_file.*': {'queue': 'import'},
             'app.tasks.thumbnail.*': {'queue': 'thumbnail'},
             'app.tasks.sidecar.*': {'queue': 'sidecar'},
+
+            # ML inference tasks - handled by ml-worker
+            'app.tasks.ml.*': {'queue': 'ml'},
         },
 
         # Task default queue for unrouted tasks