feat: language dropdowns on versions and on the game page

- Each ready version gets a "Languages" dropdown next to Play: the original language
  first, then translations with their completion; picking one starts the version in
  that language
- The game header gets the same dropdown, aggregated over published, ready versions.
  Each language points at the version that has it best (most complete, the main
  version on a tie); an original language counts as complete
- The old row of language tags linking to the translation editor is replaced
- Backend: versions carry source_name (the name of the original language)
- pages/languages.ts holds the aggregation logic with tests; LanguageMenu closes on
  outside click and Escape

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/app/schemas.py

@@ -82,6 +82,7 @@ class VersionOut(ORM):
     kind: str = "original"
     # from the version's game.json (filled by the game detail endpoint)
     source_lang: str | None = None
+    source_name: str | None = None
     languages: list[dict[str, Any]] = []
 
 

backend/app/translation.py

@@ -127,10 +127,12 @@ def _image_file(images: dict[str, Any], img: dict[str, Any] | None) -> str | Non
 def version_languages(manifest: dict[str, Any] | None) -> dict[str, Any]:
     """Source language and translations of a version, for listings."""
     if not manifest or "game.json" not in manifest.get("files", {}):
-        return {"source_lang": None, "languages": []}
+        return {"source_lang": None, "source_name": None, "languages": []}
     game = file_json(manifest, "game.json")
+    source = game.get("sourceLang")
     return {
-        "source_lang": game.get("sourceLang"),
+        "source_lang": source,
+        "source_name": LANG_NAMES.get(source, source) if source and source != "und" else None,
         "languages": [{"code": code, "name": info.get("name", code),
                        "progress": info.get("progress", 0)}
                       for code, info in sorted((game.get("locales") or {}).items())],