Reduce duplication across assets module

- Extract validate_blake3_hash() into helpers.py, used by upload, schemas, routes
- Extract get_reference_with_owner_check() into queries, used by 4 service functions
- Extract build_prefix_like_conditions() into queries/common.py, used by 3 queries
- Replace 3 inlined tag queries with get_reference_tags() calls
- Consolidate AddTagsDict/RemoveTagsDict TypedDicts into AddTagsResult/RemoveTagsResult
  dataclasses, eliminating manual field copying in tagging.py
- Make iter_row_chunks delegate to iter_chunks
- Inline trivial compute_filename_for_reference wrapper (unused session param)
- Remove mark_assets_missing_outside_prefixes pass-through in bulk_ingest.py
- Clean up unused imports (os, time, dependencies_available)
- Disable assets routes on DB init failure in main.py

Amp-Thread-ID: https://ampcode.com/threads/T-019cb649-dd4e-71ff-9a0e-ae517365207b
Co-authored-by: Amp <amp@ampcode.com>

tests-unit/assets_test/queries/test_tags.py

@@ -104,9 +104,9 @@ class TestSetReferenceTags:
         result = set_reference_tags(session, reference_id=ref.id, tags=["a", "b"])
         session.commit()
 
-        assert set(result["added"]) == {"a", "b"}
-        assert result["removed"] == []
-        assert set(result["total"]) == {"a", "b"}
+        assert set(result.added) == {"a", "b"}
+        assert result.removed == []
+        assert set(result.total) == {"a", "b"}
 
     def test_removes_old_tags(self, session: Session):
         asset = _make_asset(session, "hash1")
@@ -116,9 +116,9 @@ class TestSetReferenceTags:
         result = set_reference_tags(session, reference_id=ref.id, tags=["a"])
         session.commit()
 
-        assert result["added"] == []
-        assert set(result["removed"]) == {"b", "c"}
-        assert result["total"] == ["a"]
+        assert result.added == []
+        assert set(result.removed) == {"b", "c"}
+        assert result.total == ["a"]
 
     def test_replaces_tags(self, session: Session):
         asset = _make_asset(session, "hash1")
@@ -128,9 +128,9 @@ class TestSetReferenceTags:
         result = set_reference_tags(session, reference_id=ref.id, tags=["b", "c"])
         session.commit()
 
-        assert result["added"] == ["c"]
-        assert result["removed"] == ["a"]
-        assert set(result["total"]) == {"b", "c"}
+        assert result.added == ["c"]
+        assert result.removed == ["a"]
+        assert set(result.total) == {"b", "c"}
 
 
 class TestAddTagsToReference:
@@ -141,8 +141,8 @@ class TestAddTagsToReference:
         result = add_tags_to_reference(session, reference_id=ref.id, tags=["x", "y"])
         session.commit()
 
-        assert set(result["added"]) == {"x", "y"}
-        assert result["already_present"] == []
+        assert set(result.added) == {"x", "y"}
+        assert result.already_present == []
 
     def test_reports_already_present(self, session: Session):
         asset = _make_asset(session, "hash1")
@@ -152,8 +152,8 @@ class TestAddTagsToReference:
         result = add_tags_to_reference(session, reference_id=ref.id, tags=["x", "y"])
         session.commit()
 
-        assert result["added"] == ["y"]
-        assert result["already_present"] == ["x"]
+        assert result.added == ["y"]
+        assert result.already_present == ["x"]
 
     def test_raises_for_missing_reference(self, session: Session):
         with pytest.raises(ValueError, match="not found"):
@@ -169,9 +169,9 @@ class TestRemoveTagsFromReference:
         result = remove_tags_from_reference(session, reference_id=ref.id, tags=["a", "b"])
         session.commit()
 
-        assert set(result["removed"]) == {"a", "b"}
-        assert result["not_present"] == []
-        assert result["total_tags"] == ["c"]
+        assert set(result.removed) == {"a", "b"}
+        assert result.not_present == []
+        assert result.total_tags == ["c"]
 
     def test_reports_not_present(self, session: Session):
         asset = _make_asset(session, "hash1")
@@ -181,8 +181,8 @@ class TestRemoveTagsFromReference:
         result = remove_tags_from_reference(session, reference_id=ref.id, tags=["a", "x"])
         session.commit()
 
-        assert result["removed"] == ["a"]
-        assert result["not_present"] == ["x"]
+        assert result.removed == ["a"]
+        assert result.not_present == ["x"]
 
     def test_raises_for_missing_reference(self, session: Session):
         with pytest.raises(ValueError, match="not found"):