feat(enrich): fill in the original language from metadata providers

--enrich now sets Title.language when the service left it unset, so video tracks stop falling back to und. Adds original_language to MetadataResult (TMDB, TVDB, OMDb, IMDxAPI) and falls back to OMDb for --imdb, which previously did nothing while imdb_api_enabled defaults to false.

tests/core/test_enrich_language.py

@@ -0,0 +1,64 @@
+"""--enrich original-language enrichment."""
+
+from __future__ import annotations
+
+import pytest
+
+from unshackle.commands.dl import parse_language
+from unshackle.core.providers.imdbapi import primary_language as imdb_language
+from unshackle.core.providers.omdb import primary_language as omdb_language
+from unshackle.core.providers.tvdb import primary_language as tvdb_language
+
+
+@pytest.mark.parametrize(
+    ("tag", "expected"),
+    [
+        ("ja", "ja"),  # TMDB alpha-2
+        ("jpn", "ja"),  # IMDb alpha-3
+        ("pt-BR", "pt-BR"),
+        (None, None),
+        ("", None),
+        ("und", None),
+        ("xx-not-a-tag", None),
+    ],
+)
+def test_parse_language(tag: str | None, expected: str | None) -> None:
+    result = parse_language(tag)
+    assert (str(result) if result else None) == expected
+
+
+def test_imdb_language_takes_the_first_spoken_language() -> None:
+    data = {"spokenLanguages": [{"code": "jpn", "name": "Japanese"}, {"code": "eng", "name": "English"}]}
+    assert imdb_language(data) == "jpn"
+
+
+@pytest.mark.parametrize("data", [{}, {"spokenLanguages": []}, {"spokenLanguages": None}])
+def test_imdb_language_missing(data: dict) -> None:
+    assert imdb_language(data) is None
+
+
+@pytest.mark.parametrize(
+    ("names", "expected"),
+    [
+        ("Korean", "ko"),
+        ("Korean, English", "ko"),  # OMDb lists the main language first
+        ("", None),
+        ("None", None),  # OMDb's literal placeholder for unknown
+        ("Not A Language", None),
+    ],
+)
+def test_omdb_language_from_english_name(names: str, expected: str | None) -> None:
+    assert omdb_language({"Language": names}) == expected
+
+
+@pytest.mark.parametrize(
+    ("data", "expected"),
+    [
+        ({"primary_language": "kor"}, "kor"),  # /search
+        ({"originalLanguage": "kor"}, "kor"),  # /series/{id}/extended
+        ({"primary_language": ""}, None),
+        ({}, None),
+    ],
+)
+def test_tvdb_language_key_variants(data: dict, expected: str | None) -> None:
+    assert tvdb_language(data) == expected