feat(plex): classify collection-strip source (franchise/imdb/tmdb/smart)

Derive a `source` bucket per collection from the already-synced title + smart
flag (no schema change, no re-sync): external list providers (IMDb/TMDb/TVDb/
Trakt) by leading token, Plex smart lists via the smart flag, everything else a
genuine "collection". Returned on each info-page collection strip so the client
can show/hide each type independently. Adds the stripSource labels (en/hu/de).

frontend/src/i18n/locales/de/plex.json

@@ -98,6 +98,14 @@
     "customize": "Ansicht anpassen",
     "prefArtBg": "Dezenter Hintergrund",
     "prefCast": "Besetzung",
+    "stripSource": {
+      "collection": "Sammlungen",
+      "imdb": "IMDb",
+      "tmdb": "TMDb",
+      "tvdb": "TVDb",
+      "trakt": "Trakt",
+      "smart": "Smart-Listen"
+    },
     "openImdb": "Bei IMDb öffnen",
     "director": "Regie",
     "cast": "Besetzung & Crew",