Phase 9a: Schulkalender — Bundesland-Auswahl + Monatsansicht mit Ferien

Backend (school-service):
  - cal_public_event (region, event_type, name_de, name_en, start/end,
    UNIQUE(region, event_type, name_de, start_date)) — global snapshot.
  - cal_school_config (user_id PRIMARY KEY, bundesland, school year dates).
  - cal_school_event — Schul-eigene Termine; CRUD folgt in 9b.
  - GET /calendar/holidays?region=&from=&to= — Range-Query against
    cal_public_event, ordered by start_date.
  - GET / PUT /calendar/config — upsert Bundesland per User.
  - SeedFromSnapshot reads internal/seed/calendar_holidays.json on every
    boot; idempotent via the unique constraint. Async goroutine so the
    HTTP server starts immediately even if the seed file is large.

Data source:
  - scripts/calendar-snapshot.sh ruft openholidaysapi.org fuer alle 16
    Bundeslaender x 3 Schuljahre und schreibt
    school-service/internal/seed/calendar_holidays.json (854 Events,
    Stand Schuljahre 2026-2028).
  - Dockerfile kopiert das seed/-Verzeichnis ins Image, damit die
    Container-Datenbank beim ersten Start gefuellt wird.

Frontend (studio-v2):
  - /schulkalender Page mit Gradient + Blobs wie /stundenplan und
    /korrektur — gleicher Visual-Style.
  - BundeslandWizard: zeigt alle 16 Laender als Dropdown, speichert
    bei Klick die Config und switcht zur Monatsansicht.
  - MonthView: 6-Wochen-Grid Mo-So, Feiertage rose-toned, Schulferien
    amber-toned, heutiges Datum mit Indigo-Ring. Prev/Next/Heute
    Navigation.
  - lib/schulkalender/api.ts re-uses the stundenplan JWT helper so
    auth-mode wechselt nicht.
  - Sidebar bekommt einen Schulkalender-Eintrag (Icon mit Datum-Dots,
    Pfad /schulkalender) in allen 26 Sprachen.

Tests:
  - Go: 3 neue Validator-Tests (Bundesland len=5, EventType oneof,
    Pflichtfelder). 77 Tests gesamt, alle gruen.
  - Playwright: e2e/schulkalender.spec.ts mit Wizard, Save-Flow,
    MonthView-Render, Heute-Button, Sidebar-Link. Hermetisch via
    mockCalendarApi.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

studio-v2/components/Sidebar.tsx

@@ -18,6 +18,7 @@ const NAV_LABELS: Record<string, Record<string, string>> = {
   nav_woerterbuch: { de: 'Woerterbuch', en: 'Dictionary', tr: 'Sozluk', ar: '\u0627\u0644\u0642\u0627\u0645\u0648\u0633', uk: '\u0421\u043b\u043e\u0432\u043d\u0438\u043a', ru: '\u0421\u043b\u043e\u0432\u0430\u0440\u044c', pl: 'Slownik', fr: 'Dictionnaire', es: 'Diccionario', it: 'Dizionario', pt: 'Dicionario', nl: 'Woordenboek', ro: 'Dictionar', el: '\u039b\u03b5\u03be\u03b9\u03ba\u03cc', bg: '\u0420\u0435\u0447\u043d\u0438\u043a', hr: 'Rjecnik', cs: 'Slovnik', hu: 'Szotar', sv: 'Ordbok', da: 'Ordbog', fi: 'Sanakirja', sk: 'Slovnik', sl: 'Slovar', lt: 'Zodynas', lv: 'Vardnica', et: 'Sonaraamat' },
   nav_meet: { de: 'Videokonferenz', en: 'Video Call', tr: 'Gorusme', ar: '\u0645\u0643\u0627\u0644\u0645\u0629', uk: '\u0412\u0456\u0434\u0435\u043e\u0434\u0437\u0432\u0456\u043d\u043e\u043a', ru: '\u0412\u0438\u0434\u0435\u043e\u0437\u0432\u043e\u043d\u043e\u043a', pl: 'Wideorozmowa', fr: 'Visioconference', es: 'Videollamada', it: 'Videochiamata', pt: 'Videochamada', nl: 'Videogesprek', ro: 'Videoconferinta', el: '\u0392\u03b9\u03bd\u03c4\u03b5\u03bf\u03ba\u03bb\u03ae\u03c3\u03b7', bg: '\u0412\u0438\u0434\u0435\u043e\u0440\u0430\u0437\u0433\u043e\u0432\u043e\u0440', hr: 'Videopoziv', cs: 'Videohovor', hu: 'Videohivas', sv: 'Videosamtal', da: 'Videoopkald', fi: 'Videopuhelu', sk: 'Videohovor', sl: 'Videoklic', lt: 'Vaizdo skambutis', lv: 'Videozvans', et: 'Videokoone' },
   nav_stundenplan: { de: 'Stundenplan', en: 'Timetable', tr: 'Ders Programi', ar: 'جدول حصص', uk: 'Розклад', ru: 'Расписание', pl: 'Plan lekcji', fr: 'Emploi du temps', es: 'Horario', it: 'Orario', pt: 'Horario', nl: 'Rooster', ro: 'Orar', el: 'Πρόγραμμα', bg: 'Разписание', hr: 'Raspored', cs: 'Rozvrh', hu: 'Orarend', sv: 'Schema', da: 'Skema', fi: 'Lukujarjestys', sk: 'Rozvrh', sl: 'Urnik', lt: 'Tvarkarastis', lv: 'Stundu saraksts', et: 'Tunniplaan' },
+  nav_schulkalender: { de: 'Schulkalender', en: 'School Calendar', tr: 'Okul Takvimi', ar: 'تقويم المدرسة', uk: 'Шкільний календар', ru: 'Школьный календарь', pl: 'Kalendarz szkolny', fr: 'Calendrier scolaire', es: 'Calendario escolar', it: 'Calendario scolastico', pt: 'Calendario escolar', nl: 'Schoolkalender', ro: 'Calendar scolar', el: 'Σχολικό ημερολόγιο', bg: 'Училищен календар', hr: 'Skolski kalendar', cs: 'Skolni kalendar', hu: 'Iskolai naptar', sv: 'Skolkalender', da: 'Skolekalender', fi: 'Koulukalenteri', sk: 'Skolsky kalendar', sl: 'Solski koledar', lt: 'Mokyklos kalendorius', lv: 'Skolas kalendars', et: 'Koolikalender' },
   nav_companion: { de: 'KI-Assistent', en: 'AI Assistant', tr: 'Yapay Zeka', ar: '\u0645\u0633\u0627\u0639\u062f \u0630\u0643\u064a', uk: '\u0428\u0406-\u0430\u0441\u0438\u0441\u0442\u0435\u043d\u0442', ru: '\u0418\u0418-\u0430\u0441\u0441\u0438\u0441\u0442\u0435\u043d\u0442', pl: 'Asystent AI', fr: 'Assistant IA', es: 'Asistente IA', it: 'Assistente IA', pt: 'Assistente IA', nl: 'AI-assistent', ro: 'Asistent AI', el: 'AI \u0392\u03bf\u03b7\u03b8\u03cc\u03c2', bg: 'AI \u0430\u0441\u0438\u0441\u0442\u0435\u043d\u0442', hr: 'AI pomoenik', cs: 'AI asistent', hu: 'AI asszisztens', sv: 'AI-assistent', da: 'AI-assistent', fi: 'Tekoalyavustaja', sk: 'AI asistent', sl: 'AI pomoenik', lt: 'DI asistentas', lv: 'MI paligs', et: 'Tehisabiabi' },
 }
 
@@ -111,6 +112,13 @@ export function Sidebar({ selectedTab = 'dashboard', onTabChange }: SidebarProps
         <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={1.5} d="M8 7V3m8 4V3m-9 8h10M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5a2 2 0 00-2 2v12a2 2 0 002 2z" />
       </svg>
     )},
+    { id: 'schulkalender', labelKey: 'nav_schulkalender', href: '/schulkalender', icon: (
+      <svg className="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={1.5} d="M8 7V3m8 4V3M3 11h18M5 21h14a2 2 0 002-2V7a2 2 0 00-2-2H5a2 2 0 00-2 2v12a2 2 0 002 2z" />
+        <circle cx="8" cy="15" r="1.5" fill="currentColor" />
+        <circle cx="16" cy="15" r="1.5" fill="currentColor" />
+      </svg>
+    )},
     { id: 'companion', labelKey: 'nav_companion', href: '/companion', icon: (
       <svg className="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
         <circle cx="12" cy="12" r="9" strokeLinecap="round" strokeLinejoin="round" strokeWidth={1.5} />
@@ -158,6 +166,7 @@ export function Sidebar({ selectedTab = 'dashboard', onTabChange }: SidebarProps
     if (pathname === '/messages') return 'messages'
     if (pathname?.startsWith('/korrektur')) return 'korrektur'
     if (pathname?.startsWith('/stundenplan')) return 'stundenplan'
+    if (pathname?.startsWith('/schulkalender')) return 'schulkalender'
     return selectedTab
   }