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/tasks/import_file.py

@@ -364,6 +364,14 @@ def import_media_file(self, task_id: int):
         if sidecar_path:
             apply_sidecar_metadata.delay(record.id, sidecar_path)
 
+        # Queue ML inference (WD14 tagging + SigLIP embedding)
+        try:
+            from app.tasks.ml import tag_and_embed
+            tag_and_embed.apply_async(args=[record.id], queue='ml')
+        except Exception as ml_err:
+            # Never let an enqueue failure roll back an otherwise-successful import.
+            log.warning(f"Could not enqueue tag_and_embed for image {record.id}: {ml_err}")
+
         # Update batch stats
         if task.batch_id:
             from app.tasks.scan import update_batch_stats