feat: Mehrsprachigkeit EN/FR/ES via Mistral + Sprachumschalter

- Übersetzung per ministral-3b-latest (on-demand + DB-Cache)
- Sprachumschalter im Detailseiten-Header (DE/EN/FR/ES)
- ?lang= Query-Parameter auf /beitrag/<id>
- Neue translations-Tabelle mit submission_id+lang UNIQUE

app.py

@@ -4486,6 +4486,9 @@ def api_submit():
 
 @app.route("/beitrag/<int:sub_id>")
 def public_detail(sub_id: int):
+    lang = request.args.get("lang", "de")
+    if lang not in ("de", "en", "fr", "es"):
+        lang = "de"
     """Public detail view — full media, text, and metadata."""
     import base64
     db = get_db()
@@ -4558,7 +4561,10 @@ def public_detail(sub_id: int):
     except Exception:
         pass
 
-    content = (row["summary"] or row["content"] or "").strip()
+    # ── Mehrsprachigkeit ──
+    translation = get_translated_content(db, sub_id, lang, row)
+    content = translation["content"]
+    display_text = translation["display_text"]
 
     # Comments
     comment_rows = db.execute(