feat(dot_alfred/v2): bump SCHEMA_VERSION to 2 — added_at on MovieRelease

Phase 3 prep: Movie aggregate is about to become TMDB-only (no
filesystem fields). added_at is a release-time observation, not a
TMDB-aggregate concern, so it moves to MovieRelease +
MovieReleaseSidecar.

- Add added_at: datetime (required) to MovieRelease with a
  type-check in __post_init__.
- Add added_at: datetime (required) to MovieReleaseSidecar.
- Bump SCHEMA_VERSION 1 → 2 with a version-history note.
- Bridge round-trips added_at via Pydantic mode="json" (datetime
  → ISO 8601 string).
- Tests: update MovieRelease fixtures, add a validator test, add
  an added_at round-trip test, switch hard-coded `1` assertions
  to SCHEMA_VERSION for future-proofing.

No v1 sidecars in the wild yet — no migration code needed.

tests/domain/releases/test_entities.py

@@ -1,6 +1,7 @@
 """Tests for the releases domain entities."""
 
 import dataclasses
+from datetime import UTC, datetime
 
 import pytest
 
@@ -17,6 +18,8 @@ from alfred.domain.shared.media import AudioTrack, SubtitleTrack
 from alfred.domain.shared.value_objects import FilePath, ImdbId, TmdbId
 from alfred.domain.tv_shows.value_objects import EpisodeNumber, SeasonNumber
 
+_ADDED_AT = datetime(2026, 5, 25, 8, 30, 0, tzinfo=UTC)
+
 
 # ---------------------------------------------------------------------------
 # Helpers
@@ -238,9 +241,11 @@ class TestMovieRelease:
             imdb_id=ImdbId("tt1375666"),
             folder="Inception.2010.1080p.BluRay.x264-GROUP",
             file_path=FilePath("Inception.2010.1080p.BluRay.x264-GROUP.mkv"),
+            added_at=_ADDED_AT,
         )
         assert m.tmdb_id == TmdbId(27205)
         assert m.imdb_id == ImdbId("tt1375666")
+        assert m.added_at == _ADDED_AT
 
     def test_optional_imdb(self):
         m = MovieRelease(
@@ -248,6 +253,7 @@ class TestMovieRelease:
             imdb_id=None,
             folder="X",
             file_path=FilePath("x.mkv"),
+            added_at=_ADDED_AT,
         )
         assert m.imdb_id is None
 
@@ -258,6 +264,7 @@ class TestMovieRelease:
                 imdb_id=None,
                 folder="X",
                 file_path=FilePath("x.mkv"),
+                added_at=_ADDED_AT,
             )
 
     def test_folder_must_be_non_empty(self):
@@ -267,4 +274,15 @@ class TestMovieRelease:
                 imdb_id=None,
                 folder="",
                 file_path=FilePath("x.mkv"),
+                added_at=_ADDED_AT,
+            )
+
+    def test_added_at_must_be_datetime(self):
+        with pytest.raises(ValidationError):
+            MovieRelease(
+                tmdb_id=TmdbId(27205),
+                imdb_id=None,
+                folder="X",
+                file_path=FilePath("x.mkv"),
+                added_at="2026-05-25",  # type: ignore[arg-type]
             )