Phase 9b: Schul-Events CRUD + Schuljahres-Rollover

Backend (school-service):
  - calendar_events.go — Create/List/Delete on cal_school_event with
    UUID[] handling for affected_class_ids. Default lead-days [7,1]
    if caller omits the array.
  - calendar_rollover.go — single-transaction promotion: graduating
    classes (grade >= 13) get deleted first so the +1 update doesn't
    bump them to invalid grade 14. defaultSchoolYearDates() picks the
    next Aug-Jul pair when the caller doesn't specify.
  - Handlers + routes: GET/POST /calendar/events,
    DELETE /calendar/events/:id, POST /calendar/school-year-rollover.

Frontend (studio-v2):
  - EventModal: form with Title / Typ / Datum/Zeit / unterrichtsfrei /
    Beschreibung / Sichtbarkeit + Notification-Checkboxen. Per-Type
    Farb-Mapping in types.ts.
  - DayDetail: Modal das beim Klick auf einen Kalender-Tag aufgeht und
    Feiertage + Schulferien + Schul-Events fuer diesen Tag listet,
    inkl. Loeschen-Button pro Event.
  - RolloverWizard: zwei-Schritt-Dialog mit Datums-Auswahl + Tipp-
    Bestaetigung ("SCHULJAHR WECHSELN") gegen versehentliche Auslo-
    sung, danach Ergebnis-Card mit promoted/graduated-Counts.
  - MonthView gewinnt onDayClick + onAddEvent + onRollover Props,
    rendert farb-codierte Punkte fuer School-Events am Tagesrand.
  - Page laed Events parallel mit Holidays und reicht alle Handler
    nach unten.

Tests:
  - Go: 3 neue Tests fuer defaultSchoolYearDates + parseClassIDs.
    Validator-Test fuer CreateSchoolEventRequest existiert bereits.
    80 Subtests gesamt, alle gruen.
  - Playwright: mockCalendarApi gewinnt Routes fuer events GET/POST/
    DELETE und school-year-rollover. 6 neue Tests (EventModal open,
    submit, DayDetail open, Rollover-Trigger, Confirm-Schutz,
    Ergebnis-Anzeige).

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

school-service/internal/models/calendar.go

@@ -78,3 +78,20 @@ type CreateSchoolEventRequest struct {
 	NotifyStudents       bool     `json:"notify_students"`
 	NotificationLeadDays []int    `json:"notification_lead_days"`
 }
+
+// SchoolYearRolloverRequest moves all classes up by one grade and updates
+// the config's school-year dates. Optional date pair, otherwise defaults
+// to next Aug 01 → following Jul 31.
+type SchoolYearRolloverRequest struct {
+	NewYearStart *string `json:"new_year_start,omitempty"` // YYYY-MM-DD
+	NewYearEnd   *string `json:"new_year_end,omitempty"`
+}
+
+// SchoolYearRolloverResult is what the endpoint returns so the UI can show
+// "promoted 8 classes, removed 2 graduating ones".
+type SchoolYearRolloverResult struct {
+	ClassesPromoted  int    `json:"classes_promoted"`
+	ClassesGraduated int    `json:"classes_graduated"`
+	NewYearStart     string `json:"new_year_start"`
+	NewYearEnd       string `json:"new_year_end"`
+}