feat: reporting dashboard — case stats, deadline compliance, workload, billing (P1)

Backend:
- ReportingService with aggregation queries (CTEs, FILTER clauses)
- 4 API endpoints: /api/reports/{cases,deadlines,workload,billing}
- Date range filtering via ?from=&to= query params

Frontend:
- /berichte page with 4 tabs: Akten, Fristen, Auslastung, Abrechnung
- recharts: bar/pie/line charts for all report types
- Date range picker, CSV export, print-friendly view
- Sidebar nav entry with BarChart3 icon

Also resolves merge conflicts between role-based, notification, and
audit trail branches, and adds missing TS types (AuditLogResponse,
Notification, NotificationPreferences).

backend/internal/auth/tenant_resolver_test.go

@@ -10,49 +10,34 @@ import (
 )
 
 type mockTenantLookup struct {
-<<<<<<< HEAD
 	tenantID  *uuid.UUID
 	err       error
 	hasAccess bool
 	accessErr error
-||||||| 82878df
-	tenantID *uuid.UUID
-	err      error
-=======
-	tenantID *uuid.UUID
-	role     string
-	err      error
->>>>>>> mai/pike/p0-role-based
+	role      string
 }
 
 func (m *mockTenantLookup) FirstTenantForUser(ctx context.Context, userID uuid.UUID) (*uuid.UUID, error) {
 	return m.tenantID, m.err
 }
 
-<<<<<<< HEAD
 func (m *mockTenantLookup) VerifyAccess(ctx context.Context, userID, tenantID uuid.UUID) (bool, error) {
 	return m.hasAccess, m.accessErr
 }
 
-||||||| 82878df
-=======
 func (m *mockTenantLookup) GetUserRole(ctx context.Context, userID, tenantID uuid.UUID) (string, error) {
 	if m.role != "" {
 		return m.role, m.err
 	}
-	return "associate", m.err
+	if m.hasAccess {
+		return "associate", m.err
+	}
+	return "", m.err
 }
 
->>>>>>> mai/pike/p0-role-based
 func TestTenantResolver_FromHeader(t *testing.T) {
 	tenantID := uuid.New()
-<<<<<<< HEAD
-	tr := NewTenantResolver(&mockTenantLookup{hasAccess: true})
-||||||| 82878df
-	tr := NewTenantResolver(&mockTenantLookup{})
-=======
-	tr := NewTenantResolver(&mockTenantLookup{role: "partner"})
->>>>>>> mai/pike/p0-role-based
+	tr := NewTenantResolver(&mockTenantLookup{hasAccess: true, role: "partner"})
 
 	var gotTenantID uuid.UUID
 	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {