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")

backend/tests/test_collaboration.py

@@ -289,6 +289,39 @@ def test_import_dedupes_by_uid(client):
     assert imported and imported[0]["creator"]["display_name"] == "Max Mustermann (importiert)"
 
 
+DUP_UID_ICS = b"""BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Nextcloud
+BEGIN:VEVENT
+UID:recurring@nc
+SUMMARY:Standup
+DTSTART:20260601T090000Z
+DTEND:20260601T091500Z
+RRULE:FREQ=WEEKLY;BYDAY=MO
+END:VEVENT
+BEGIN:VEVENT
+UID:recurring@nc
+RECURRENCE-ID:20260608T090000Z
+SUMMARY:Standup verschoben
+DTSTART:20260608T100000Z
+DTEND:20260608T101500Z
+END:VEVENT
+END:VCALENDAR
+"""
+
+
+def test_import_handles_duplicate_uid_in_file(client):
+    """Nextcloud exports recurring events as multiple VEVENTs sharing a UID;
+    importing must not 500 on the unique constraint."""
+    admin = register_admin(client)
+    cal_id = _make_calendar(client, admin, "NC")
+    files = {"file": ("nc.ics", DUP_UID_ICS, "text/calendar")}
+    r = client.post(f"/api/local/calendars/{cal_id}/import", headers=auth(admin), files=files)
+    assert r.status_code == 200, r.text
+    body = r.json()
+    assert body["imported"] == 1 and body["skipped"] == 1
+
+
 def test_export_contains_organizer_and_rrule(client):
     admin = register_admin(client)
     cal_id = _make_calendar(client, admin, "Export-Test")