feat(library): descriptive metadata on every entry — platform, year, genres, and friends

Emulation-and-beyond libraries need more than a title and a poster. Every
library shape (GameEntry, CustomEntry, CustomInput, ProviderEntryInput)
now carries a shared, flattened GameMeta: platform, description,
developer, publisher, release_year, genres, tags, region, players. All
fields are optional and flat on the wire, so existing library.json files,
provider plugins, and clients keep working unchanged.

- Installed-store scanners (Steam, Lutris, Heroic, Epic, GOG, Xbox) stamp
  platform=PC; custom/provider entries carry whatever was authored.
- GET /library grows a ?platform= filter (case-insensitive) beside
  ?provider=.
- Console: the add/edit form gets a Details section (round-tripping every
  field, since update replaces the entry), the poster tile a platform
  badge (non-PC only — the store badge already implies PC) and the year.
- plugin-kit: ProviderEntry accepts the same fields (new GameMeta schema,
  spread flat); SDK + OpenAPI spec regenerated.
- pf-client-core decodes platform for future client badges.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/messages/de.json

@@ -187,6 +187,20 @@
 	"library_field_logo": "Logo-Bild-URL",
 	"library_field_command": "Startbefehl",
 	"library_field_command_help": "Optional. Der Befehl, mit dem der Host diesen Titel startet.",
+	"library_field_platform": "Plattform",
+	"library_field_platform_help": "Das System, auf dem dieser Titel läuft, z. B. PS2, Xbox 360, SNES, PC.",
+	"library_field_description": "Beschreibung",
+	"library_field_developer": "Entwickler",
+	"library_field_publisher": "Publisher",
+	"library_field_release_year": "Erscheinungsjahr",
+	"library_field_genres": "Genres",
+	"library_field_genres_help": "Kommagetrennt, z. B. RPG, Plattformer.",
+	"library_field_tags": "Tags",
+	"library_field_tags_help": "Kommagetrennte Labels zum Organisieren, z. B. Koop, Kinder.",
+	"library_field_region": "Region",
+	"library_field_region_help": "z. B. NTSC-U, PAL, NTSC-J.",
+	"library_field_players": "Spieler",
+	"library_details_legend": "Details (optional)",
 	"library_save": "Speichern",
 	"library_create": "Hinzufügen",
 	"library_cancel": "Abbrechen",

web/messages/en.json

@@ -187,6 +187,20 @@
 	"library_field_logo": "Logo art URL",
 	"library_field_command": "Launch command",
 	"library_field_command_help": "Optional. The command the host runs to launch this title.",
+	"library_field_platform": "Platform",
+	"library_field_platform_help": "The system this title runs on, e.g. PS2, Xbox 360, SNES, PC.",
+	"library_field_description": "Description",
+	"library_field_developer": "Developer",
+	"library_field_publisher": "Publisher",
+	"library_field_release_year": "Release year",
+	"library_field_genres": "Genres",
+	"library_field_genres_help": "Comma-separated, e.g. RPG, Platformer.",
+	"library_field_tags": "Tags",
+	"library_field_tags_help": "Comma-separated labels for organizing, e.g. co-op, kids.",
+	"library_field_region": "Region",
+	"library_field_region_help": "e.g. NTSC-U, PAL, NTSC-J.",
+	"library_field_players": "Players",
+	"library_details_legend": "Details (optional)",
 	"library_save": "Save",
 	"library_create": "Add",
 	"library_cancel": "Cancel",