feat(releases): Phase 1 — new filesystem release domain + TmdbId VO

First step of specs/dot_alfred_v2.md. Introduces a separate bounded
context (alfred/domain/releases/) for the filesystem-side aggregates,
disjoint from TMDB identity which stays in tv_shows/ and movies/.
The link between the two worlds is TmdbId, used as the natural key
in the persistence layer (no domain-level reference).

New package alfred/domain/releases/:
- value_objects: EpisodeRange (covers SxxE01E02E03 multi-episode
  files via start/end inclusive range, with count/numbers/is_single
  helpers), ReleaseMode enum (PACK = N video files direct in the
  season folder, EPISODIC = N sub-folders).
- entities: TrackProfile, EpisodeRelease, SeasonRelease (with
  episode_count() summing each EpisodeRange.count()), SeriesRelease
  (tmdb_id primary anchor, optional imdb_id secondary), MovieRelease.
  All frozen dataclasses.
- builders: SeasonReleaseBuilder + SeriesReleaseBuilder mirroring
  the v1 TVShowBuilder pattern. Builders sort episodes by range
  start on emit and reject overlapping ranges (two files claiming
  the same TMDB slot). from_existing() seeds a builder from an
  existing frozen aggregate for round-trip edits.
- repositories: abstract ports (SeriesReleaseRepository,
  MovieReleaseRepository); concrete .alfred sidecar impls arrive
  in Phase 2.

New shared VO alfred/domain/shared/value_objects.py::TmdbId — positive
int, rejects bool/str/float, symmetric with the existing ImdbId VO.

73 unit tests cover VO validation, entity invariants, builder sort
+ overlap detection, and from_existing() round-trips.

v1 code paths are untouched at this stage; the new domain coexists
with the old TVShow aggregate until Phase 3 refactors it.

tests/domain/test_shared_value_objects.py

@@ -1,11 +1,11 @@
-"""Tests for shared domain value objects: ImdbId, FilePath, FileSize."""
+"""Tests for shared domain value objects: ImdbId, TmdbId, FilePath, FileSize."""
 
 from pathlib import Path
 
 import pytest
 
 from alfred.domain.shared.exceptions import ValidationError
-from alfred.domain.shared.value_objects import FilePath, FileSize, ImdbId
+from alfred.domain.shared.value_objects import FilePath, FileSize, ImdbId, TmdbId
 
 # ---------------------------------------------------------------------------
 # ImdbId
@@ -54,6 +54,53 @@ class TestImdbId:
         assert len(ids) == 2
 
 
+# ---------------------------------------------------------------------------
+# TmdbId
+# ---------------------------------------------------------------------------
+
+
+class TestTmdbId:
+    def test_valid_int(self):
+        tid = TmdbId(84958)
+        assert tid.value == 84958
+        assert str(tid) == "84958"
+        assert int(tid) == 84958
+
+    def test_zero_raises(self):
+        with pytest.raises(ValidationError):
+            TmdbId(0)
+
+    def test_negative_raises(self):
+        with pytest.raises(ValidationError):
+            TmdbId(-1)
+
+    def test_string_raises(self):
+        with pytest.raises(ValidationError):
+            TmdbId("84958")  # type: ignore[arg-type]
+
+    def test_float_raises(self):
+        with pytest.raises(ValidationError):
+            TmdbId(84958.0)  # type: ignore[arg-type]
+
+    def test_bool_raises(self):
+        # bool is a subclass of int — make sure we reject it explicitly.
+        with pytest.raises(ValidationError):
+            TmdbId(True)  # type: ignore[arg-type]
+        with pytest.raises(ValidationError):
+            TmdbId(False)  # type: ignore[arg-type]
+
+    def test_repr(self):
+        assert repr(TmdbId(84958)) == "TmdbId(84958)"
+
+    def test_equality(self):
+        assert TmdbId(84958) == TmdbId(84958)
+        assert TmdbId(84958) != TmdbId(12345)
+
+    def test_hashable(self):
+        ids = {TmdbId(84958), TmdbId(12345), TmdbId(84958)}
+        assert len(ids) == 2
+
+
 # ---------------------------------------------------------------------------
 # FilePath
 # ---------------------------------------------------------------------------