refactor(release): freeze ParsedRelease + enrich_from_probe returns new instance

ParsedRelease is now @dataclass(frozen=True). The enrichment passes that
used to patch fields in place now produce new instances:

- enrich_from_probe(parsed, info, kb) returns a new ParsedRelease via
  dataclasses.replace (no allocation when no field changed).
- inspect_release rebinds 'parsed' after detect_media_type (wrapped in
  MediaTypeToken — the strict isinstance check now also runs on
  replace) and after enrich_from_probe.

languages becomes a tuple[str, ...] so the VO is properly immutable.
Parser pipeline packs languages as a tuple in the assemble dict.

Callers updated: inspect_release, testing/recognize_folders_in_downloads.py.
Tests updated: 22 enrich_from_probe call sites rebound, language
assertions switched to tuple literals, test_release_fixtures normalizes
result['languages'] back to list for YAML-fixture comparison.

Suite: 1077 passed.

tests/domain/test_release.py

@@ -264,10 +264,10 @@ class TestParsedReleaseInvariants:
         r = _parse(raw)
         assert r.raw == raw
 
-    def test_languages_defaults_to_empty_list_not_none(self):
+    def test_languages_defaults_to_empty_tuple_not_none(self):
         r = _parse("Movie.2020.1080p.BluRay.x264-GRP")
-        # __post_init__ ensures languages is a list, never None
-        assert r.languages == []
+        # ``languages`` defaults to an empty tuple (frozen VO).
+        assert r.languages == ()
 
     def test_tech_string_joined(self):
         r = _parse("Movie.2020.1080p.BluRay.x264-GRP")