feat: add deadline management frontend (Phase 1G)

- Fristen page with list view (sortable, filterable by status/case)
- Calendar view with month navigation and deadline dots
- Deadline calculator page (proceeding type + trigger date = timeline)
- Traffic light urgency: red (overdue), amber (this week), green (OK)
- Backend: GET /api/deadlines (all tenant deadlines), GET /api/proceeding-types
- API client: added patch() method
- Types: DeadlineRule, ProceedingType, CalculatedDeadline, RuleTreeNode

backend/internal/handlers/deadlines.go

@@ -20,6 +20,23 @@ func NewDeadlineHandlers(ds *services.DeadlineService, db *sqlx.DB) *DeadlineHan
 	return &DeadlineHandlers{deadlines: ds, db: db}
 }
 
+// ListAll handles GET /api/deadlines
+func (h *DeadlineHandlers) ListAll(w http.ResponseWriter, r *http.Request) {
+	tenantID, err := resolveTenant(r, h.db)
+	if err != nil {
+		handleTenantError(w, err)
+		return
+	}
+
+	deadlines, err := h.deadlines.ListAll(tenantID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to list deadlines")
+		return
+	}
+
+	writeJSON(w, http.StatusOK, deadlines)
+}
+
 // ListForCase handles GET /api/cases/{caseID}/deadlines
 func (h *DeadlineHandlers) ListForCase(w http.ResponseWriter, r *http.Request) {
 	tenantID, err := resolveTenant(r, h.db)