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

requirements-ml.txt

@@ -0,0 +1,21 @@
+# Base app deps (mirrors requirements.txt so the ml-worker can import app code).
+# Floors reflect recent-stable baselines — update them proactively when you bump the main requirements.txt
+# so a future minor release of any dep can't pull the ml-worker below a version we've actually tested.
+Flask>=3.0
+Flask-SQLAlchemy>=3.1
+Flask-Migrate>=4.0
+psycopg2-binary>=2.9
+pillow>=10.4
+exifread>=3.0
+imagehash>=4.3
+gunicorn>=22.0
+celery[redis]>=5.4.0
+redis>=5.1.0
+pgvector>=0.3.0
+
+# ML-specific deps (CPU-only)
+numpy>=1.26                # transformers 4.45+/torch 2.4+ accept numpy 2.x
+onnxruntime>=1.19          # CPU build; do not install onnxruntime-gpu here
+transformers>=4.45
+huggingface_hub>=0.25
+sentencepiece>=0.2.0       # required by SiglipTokenizer