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>

school-service/internal/services/calendar_service_test.go

@@ -0,0 +1,64 @@
+package services
+
+import (
+	"testing"
+
+	"github.com/breakpilot/school-service/internal/models"
+)
+
+func TestUpsertSchoolCalendarConfigRequest_Validation(t *testing.T) {
+	tests := []struct {
+		name    string
+		req     models.UpsertSchoolCalendarConfigRequest
+		wantErr bool
+	}{
+		{"valid NI", models.UpsertSchoolCalendarConfigRequest{Bundesland: "DE-NI"}, false},
+		{"empty bundesland", models.UpsertSchoolCalendarConfigRequest{Bundesland: ""}, true},
+		{"too long", models.UpsertSchoolCalendarConfigRequest{Bundesland: "DE-NIE"}, true},
+		{"too short", models.UpsertSchoolCalendarConfigRequest{Bundesland: "DE"}, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if (validate.Struct(tt.req) != nil) != tt.wantErr {
+				t.Errorf("unexpected validation outcome for %s", tt.name)
+			}
+		})
+	}
+}
+
+func TestCreateSchoolEventRequest_Validation(t *testing.T) {
+	tests := []struct {
+		name    string
+		req     models.CreateSchoolEventRequest
+		wantErr bool
+	}{
+		{"valid fortbildung", models.CreateSchoolEventRequest{
+			Title: "SCHILF", EventType: "fortbildung",
+			StartDate: "2026-10-01", EndDate: "2026-10-01",
+		}, false},
+		{"missing title", models.CreateSchoolEventRequest{
+			EventType: "fortbildung", StartDate: "2026-10-01", EndDate: "2026-10-01",
+		}, true},
+		{"invalid event type", models.CreateSchoolEventRequest{
+			Title: "X", EventType: "wedding",
+			StartDate: "2026-10-01", EndDate: "2026-10-01",
+		}, true},
+		{"missing dates", models.CreateSchoolEventRequest{
+			Title: "X", EventType: "schulfeier",
+		}, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if (validate.Struct(tt.req) != nil) != tt.wantErr {
+				t.Errorf("unexpected validation outcome for %s", tt.name)
+			}
+		})
+	}
+}
+
+func TestNewCalendarService_Constructs(t *testing.T) {
+	s := NewCalendarService(nil)
+	if s == nil {
+		t.Fatal("expected non-nil service")
+	}
+}