feat(suggestions): user-managed blocklist for noisy auto-tags

Adds a tag_suggestion_blocklist table + service-layer filter so the
user can permanently suppress specific canonical tag names from the
suggestion stream (WD14 anatomy/composition tags like '1girl',
'breasts', 'nipples' that aren't useful for the discoverability use
case this app targets).

Data model
  - migration k26042201: tag_suggestion_blocklist(name TEXT PK, created_at)
  - model TagSuggestionBlocklistEntry

Service
  - tag_suggestions._blocklisted_names() snapshots the current set
  - get_suggestions filters merged results before grouping, so both
    WD14- and embedding-sourced suggestions respect the blocklist
  - get_bulk_suggestions inherits the filter via its per-image call
    to get_suggestions

API
  - GET  /api/suggestions/blocklist           -> {ok, names}
  - POST /api/suggestions/blocklist           -> add one
  - POST /api/suggestions/blocklist/delete    -> remove one
  - POST /api/suggestions/blocklist/bulk      -> replace the whole list
    (backs the settings textarea save button)

UI
  - modal suggestion chip gets a third action button (⊘) alongside
    accept (✓) / reject (✕). Clicking it adds the name to the
    blocklist, logs a rejection for ML feedback on this image, and
    sweeps every chip on the page carrying that same name.
  - Settings -> Maintenance -> Suggestion blocklist section with a
    monospaced textarea (one name per line) + Save. Loads current
    entries on mount.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

migrations/versions/k26042201_add_tag_suggestion_blocklist.py

@@ -0,0 +1,38 @@
+"""Create tag_suggestion_blocklist table.
+
+User-managed blocklist of canonical tag names that should never appear as
+auto-suggestions. Filters WD14 + embedding results in get_suggestions before
+grouping. Name is the primary key (exact-match against the canonicalized
+WD14 output).
+
+Revision ID: k26042201
+Revises: j26042101
+Create Date: 2026-04-22
+"""
+from __future__ import annotations
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = 'k26042201'
+down_revision = 'j26042101'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_table(
+        'tag_suggestion_blocklist',
+        sa.Column('name', sa.Text(), primary_key=True),
+        sa.Column(
+            'created_at',
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+    )
+
+
+def downgrade():
+    op.drop_table('tag_suggestion_blocklist')