feat(.alfred v2 — Phase 2): Pydantic sidecars, atomic repos, auto-heal index

Spec: specs/dot_alfred_v2.md (Phase 2).

New package alfred/infrastructure/persistence/dot_alfred/v2/:
  * sidecar_release.py / sidecar_root.py — Pydantic DTOs
    (extra="forbid", frozen=True) for per-item sidecars and the
    library-root index. schema_version enforced via model_validator.
  * serializer.py — read_yaml / atomic_write_yaml (.tmp + os.replace).
    SidecarSchemaError wraps YAML + Pydantic errors uniformly.
  * bridge.py — lossless domain <-> sidecar for SeriesRelease /
    MovieRelease; projection-only show_index_entry_from /
    movie_index_entry_from with multi-episode-file flattening.
  * repository.py — DotAlfredSeriesReleaseRepository /
    DotAlfredMovieReleaseRepository (log+skip on corruption),
    DotAlfredTVShowLibraryIndex / DotAlfredMovieLibraryIndex with
    silent auto-heal on missing/corrupt index reads. Writes never
    auto-heal (read paths handle that).

TMDB client extensions:
  * TmdbSeasonInfo / TmdbShowInfo DTOs + pure parse_tv_show_info.
  * TMDBClient.get_tv_show_info aggregates /tv/{id} +
    /tv/{id}/external_ids.

Domain change:
  * SubtitleTrack gains is_sdh: bool = False, populated from
    ffprobe's hearing_impaired disposition. Required for v2 sidecar
    parity (spec replaces v1's type: "sdh" with explicit flag).
    Default keeps every existing caller unchanged.

Tests: 37 new v2 integration tests on tmp_path (round-trips, atomic
writes, schema mismatch handling, anchor warnings, auto-heal paths)
plus 16 TMDB DTO tests. Full suite: 1240 -> 1277 passed.

Implementation notes filed in .claude/specs/dot_alfred_v2_notes.md
(strict=True trade-off, upsert signature deviation from spec, etc.).

Phases 3-5 (TVShow/Movie refactor to TMDB-only, rescan_show rewrite,
v1 deletion + wiring) are next.

tests/infrastructure/persistence/dot_alfred/v2/test_round_trip.py

@@ -0,0 +1,91 @@
+"""Round-trip tests — domain → sidecar → YAML → sidecar → domain.
+
+These tests are the contract guarantee that the v2 sidecar is a
+lossless cache for everything the spec claims it stores. Any field
+introduced in the future must come with a round-trip test that
+covers it; otherwise we can silently drop it on read.
+"""
+
+from __future__ import annotations
+
+import yaml
+
+from alfred.infrastructure.persistence.dot_alfred.v2.bridge import (
+    movie_release_from_sidecar,
+    movie_release_to_sidecar,
+    series_release_from_sidecar,
+    series_release_to_sidecar,
+)
+from alfred.infrastructure.persistence.dot_alfred.v2.sidecar_release import (
+    MovieReleaseSidecar,
+    SeriesReleaseSidecar,
+)
+
+
+class TestSeriesReleaseRoundTrip:
+    def test_domain_to_sidecar_preserves_top_level(self, foundation_release):
+        sidecar = series_release_to_sidecar(foundation_release)
+        assert sidecar.schema_version == 1
+        assert sidecar.tmdb_id == 84958
+        assert sidecar.imdb_id == "tt0804484"
+        assert len(sidecar.releases) == 2
+
+    def test_full_loop_domain_to_domain_is_equal(self, foundation_release):
+        sidecar = series_release_to_sidecar(foundation_release)
+        restored = series_release_from_sidecar(sidecar)
+        assert restored == foundation_release
+
+    def test_full_loop_through_yaml_is_equal(self, foundation_release):
+        sidecar = series_release_to_sidecar(foundation_release)
+        text = yaml.safe_dump(sidecar.model_dump(mode="json"))
+        reloaded = SeriesReleaseSidecar.model_validate(yaml.safe_load(text))
+        restored = series_release_from_sidecar(reloaded)
+        assert restored == foundation_release
+
+    def test_multi_episode_file_round_trips(self, foundation_release):
+        sidecar = series_release_to_sidecar(foundation_release)
+        s02 = sidecar.releases[1]
+        multi = s02.episodes[1]
+        assert multi.start == 2 and multi.end == 3
+        restored = series_release_from_sidecar(sidecar)
+        restored_multi = restored.seasons[1].episodes[1]
+        assert restored_multi.episodes.start.value == 2
+        assert restored_multi.episodes.end.value == 3
+
+    def test_sdh_flag_round_trips(self, foundation_release):
+        sidecar = series_release_to_sidecar(foundation_release)
+        restored = series_release_from_sidecar(sidecar)
+        sdh_track = restored.seasons[0].episodes[0].tracks.subtitle_tracks[1]
+        assert sdh_track.is_sdh is True
+
+    def test_no_imdb_id_round_trips_as_none(self, foundation_release):
+        # Replace the imdb_id with None and verify it survives the loop.
+        from dataclasses import replace
+        no_imdb = replace(foundation_release, imdb_id=None)
+        sidecar = series_release_to_sidecar(no_imdb)
+        assert sidecar.imdb_id is None
+        restored = series_release_from_sidecar(sidecar)
+        assert restored.imdb_id is None
+
+
+class TestMovieReleaseRoundTrip:
+    def test_domain_to_sidecar_preserves_top_level(self, inception_release):
+        sidecar = movie_release_to_sidecar(inception_release)
+        assert sidecar.schema_version == 1
+        assert sidecar.tmdb_id == 27205
+        assert sidecar.imdb_id == "tt1375666"
+        assert sidecar.folder == "Inception.2010.1080p.BluRay.x264-GROUP"
+
+    def test_full_loop_through_yaml_is_equal(self, inception_release):
+        sidecar = movie_release_to_sidecar(inception_release)
+        text = yaml.safe_dump(sidecar.model_dump(mode="json"))
+        reloaded = MovieReleaseSidecar.model_validate(yaml.safe_load(text))
+        restored = movie_release_from_sidecar(reloaded)
+        assert restored == inception_release
+
+    def test_forced_subtitle_flag_round_trips(self, inception_release):
+        sidecar = movie_release_to_sidecar(inception_release)
+        restored = movie_release_from_sidecar(sidecar)
+        forced = restored.tracks.subtitle_tracks[1]
+        assert forced.is_forced is True
+        assert forced.language == "fre"