feat(ml): clamp allowlist min_confidence to the tagger store floor

Consumer #4 of the store-floor change (#764). An allowlist tag can't
auto-apply more permissively than the ingest floor — predictions below
tagger_store_floor aren't stored, so a lower min_confidence behaves
identically to the floor. update_threshold now clamps to max(value, floor);
the AllowlistTable confidence input min-binds to the live floor and clamps
on edit. Keeps the stored threshold honest about actual apply behavior.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_ml_allowlist.py

@@ -104,3 +104,17 @@ async def test_update_threshold_and_remove(db):
     assert abs(row.min_confidence - 0.80) < 1e-6
     await svc.remove(tag.id)
     assert await db.get(TagAllowlist, tag.id) is None
+
+
+@pytest.mark.asyncio
+async def test_update_threshold_clamped_to_store_floor(db):
+    # A min_confidence below the store floor (default 0.70) is clamped up —
+    # predictions below the floor aren't stored, so a lower threshold can't
+    # apply more permissively than the floor (#764).
+    tag = await TagService(db).find_or_create("Lowthr", TagKind.general)
+    svc = AllowlistService(db)
+    img = await _make_image(db)
+    await svc.accept(img.id, tag.id)
+    await svc.update_threshold(tag.id, 0.30)
+    row = await db.get(TagAllowlist, tag.id)
+    assert abs(row.min_confidence - 0.70) < 1e-6