fix: Import-500 bei doppelten UIDs, Picker-UI & Settings-URL-State

- Import: Dedupe doppelter UIDs innerhalb der Datei (Nextcloud exportiert
  wiederkehrende Termine als mehrere VEVENTs gleicher UID) -> kein
  UNIQUE-constraint-500 mehr; Commit abgesichert. Test ergaenzt (15 gruen).
- Picker (Gruppen-Sichtbarkeit + Mitglieder): als <div>-Zeilen statt <label>,
  damit die globale ".form-group label"-Uppercase/Grau-Regel das Layout nicht
  mehr zerschiesst. Saubere .pick-row-Optik (Checkbox/Radio links, Name links).
- Einstellungen haben jetzt eigenen URL-State (#...&settings=1): Reload/Cache-
  leeren bleibt in den Einstellungen statt zur Kalenderansicht zu springen.
- Version v27.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/routers/local_router.py

@@ -386,8 +386,17 @@ def _import_ics_into(cal: models.LocalCalendar, raw: bytes, db: Session) -> dict
     parsed = ical_io.parse_ics(raw)
     imported = 0
     skipped = 0
+    errors = list(parsed["errors"])
+    # local_events.uid is globally unique. Dedupe against the DB AND within this
+    # file — e.g. Nextcloud exports recurring events as several VEVENTs sharing a
+    # UID (RECURRENCE-ID overrides), which would otherwise violate the constraint.
+    seen_uids: set[str] = set()
     for item in parsed["events"]:
         uid = item.get("uid") or str(uuid.uuid4())
+        if uid in seen_uids:
+            skipped += 1
+            continue
+        seen_uids.add(uid)
         existing = db.query(models.LocalEvent).filter(models.LocalEvent.uid == uid).first()
         if existing:
             skipped += 1
@@ -407,8 +416,12 @@ def _import_ics_into(cal: models.LocalCalendar, raw: bytes, db: Session) -> dict
         )
         db.add(ev)
         imported += 1
-    db.commit()
-    return {"imported": imported, "skipped": skipped, "errors": parsed["errors"]}
+    try:
+        db.commit()
+    except Exception as exc:
+        db.rollback()
+        raise ValueError(f"Import fehlgeschlagen: {exc}")
+    return {"imported": imported, "skipped": skipped, "errors": errors}
 
 
 @router.post("/calendars/{calendar_id}/import")