feat: implement same_base update strategy for model annotations

Add support for configurable update flag strategy with new "same_base" mode that considers base model versions when determining update availability. The strategy is controlled by the "update_flag_strategy" setting.

When strategy is set to "same_base":
- Uses get_records_bulk instead of has_updates_bulk
- Compares model versions against highest local versions per base model
- Provides more granular update detection based on base model relationships

Fallback to existing bulk or individual update checks when:
- Strategy is not "same_base"
- Bulk operations fail
- Records are unavailable

This enables more precise update flagging for models sharing common bases.

tests/services/test_model_update_service.py

@@ -52,11 +52,11 @@ class NotFoundProvider:
         return {}
 
 
-def make_version(version_id, *, in_library, should_ignore=False):
+def make_version(version_id, *, in_library, base_model=None, should_ignore=False):
     return ModelVersionRecord(
         version_id=version_id,
         name=None,
-        base_model=None,
+        base_model=base_model,
         released_at=None,
         size_bytes=None,
         preview_url=None,
@@ -147,6 +147,25 @@ def test_has_update_detects_newer_remote_version():
     assert record.has_update() is True
 
 
+def test_has_update_for_base_matches_same_base_model():
+    record = make_record(
+        make_version(5, in_library=True, base_model="Pony"),
+        make_version(6, in_library=False, base_model="Pony"),
+        make_version(7, in_library=False, base_model="Flux.1"),
+    )
+
+    assert record.has_update_for_base(5, "Pony") is True
+
+
+def test_has_update_for_base_rejects_other_base_models():
+    record = make_record(
+        make_version(10, in_library=True, base_model="Flux"),
+        make_version(20, in_library=False, base_model="SDXL"),
+    )
+
+    assert record.has_update_for_base(10, "Flux") is False
+
+
 @pytest.mark.asyncio
 async def test_refresh_persists_versions_and_uses_cache(tmp_path):
     db_path = tmp_path / "updates.sqlite"