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/handlers/calendar_handlers.go

@@ -0,0 +1,76 @@
+package handlers
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/breakpilot/school-service/internal/models"
+	"github.com/gin-gonic/gin"
+)
+
+// ListCalendarHolidays returns OpenHolidaysAPI events for a region + range.
+// Query params: ?region=DE-NI&from=2026-08-01&to=2027-07-31. If omitted,
+// region falls back to the caller's saved config and the range to the
+// current calendar year.
+func (h *Handler) ListCalendarHolidays(c *gin.Context) {
+	uid := getUserID(c)
+	if uid == "" {
+		respondError(c, http.StatusUnauthorized, "User not authenticated")
+		return
+	}
+	region := c.Query("region")
+	if region == "" {
+		cfg, err := h.calendarService.GetConfig(c.Request.Context(), uid)
+		if err != nil || cfg == nil {
+			respondError(c, http.StatusBadRequest, "region query param required (no saved config)")
+			return
+		}
+		region = cfg.Bundesland
+	}
+	from := c.DefaultQuery("from", time.Now().Format("2006-01-02"))
+	to := c.DefaultQuery("to", time.Now().AddDate(1, 0, 0).Format("2006-01-02"))
+
+	events, err := h.calendarService.ListHolidays(c.Request.Context(), region, from, to)
+	if err != nil {
+		respondError(c, http.StatusInternalServerError, "Failed to load holidays: "+err.Error())
+		return
+	}
+	if events == nil {
+		events = []models.PublicEvent{}
+	}
+	respondSuccess(c, events)
+}
+
+func (h *Handler) GetCalendarConfig(c *gin.Context) {
+	uid := getUserID(c)
+	if uid == "" {
+		respondError(c, http.StatusUnauthorized, "User not authenticated")
+		return
+	}
+	cfg, err := h.calendarService.GetConfig(c.Request.Context(), uid)
+	if err != nil {
+		// No row → 200 with null so the wizard knows to prompt.
+		respondSuccess(c, nil)
+		return
+	}
+	respondSuccess(c, cfg)
+}
+
+func (h *Handler) UpsertCalendarConfig(c *gin.Context) {
+	uid := getUserID(c)
+	if uid == "" {
+		respondError(c, http.StatusUnauthorized, "User not authenticated")
+		return
+	}
+	var req models.UpsertSchoolCalendarConfigRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		respondError(c, http.StatusBadRequest, "Invalid request: "+err.Error())
+		return
+	}
+	cfg, err := h.calendarService.UpsertConfig(c.Request.Context(), uid, &req)
+	if err != nil {
+		respondError(c, http.StatusInternalServerError, "Failed to save config: "+err.Error())
+		return
+	}
+	respondCreated(c, cfg)
+}