feat: scheduled report digests + per-session capacity (M33)

POST /v1/internal/jobs/reports/dispatch emails each tenant owner a
trailing-window digest (bookings, revenue, per-service and per-staff
breakdown) localized to the tenant locale; zero-activity tenants are
skipped. Metrics cores extracted to tenant-scoped variants so the job
needs no principal.

PATCH /v1/catalog/class-sessions/:id sets a session's seat count with
a confirmed-bookings floor — shrinking below it needs allowOverCapacity,
matching the waitlist-promotion convention. Session rows gain an inline
capacity editor with an overbook confirm state.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/db/repository.go

@@ -30,6 +30,9 @@ type Repository interface {
 	GetClassSessionByID(ctx context.Context, sessionID string) (ClassSessionRecord, error)
 	CreateClassSession(ctx context.Context, params CreateClassSessionParams) (ClassSessionRecord, error)
 	DeleteClassSession(ctx context.Context, sessionID string) error
+	// UpdateClassSessionCapacity sets the session's seat count; the caller
+	// checks tenancy and the booked-seats floor.
+	UpdateClassSessionCapacity(ctx context.Context, sessionID string, capacity int) (ClassSessionRecord, error)
 	ListClassTemplatesByTenant(ctx context.Context, tenantID string) ([]ClassTemplateRecord, error)
 	GetClassTemplateByID(ctx context.Context, templateID string) (ClassTemplateRecord, error)
 	CreateClassTemplate(ctx context.Context, params CreateClassTemplateParams) (ClassTemplateRecord, error)
@@ -1539,6 +1542,16 @@ func (r *MemoryRepository) DeleteClassSession(_ context.Context, sessionID strin
 	return pgx.ErrNoRows
 }
 
+func (r *MemoryRepository) UpdateClassSessionCapacity(_ context.Context, sessionID string, capacity int) (ClassSessionRecord, error) {
+	for i := range r.classSessions {
+		if r.classSessions[i].ID == sessionID {
+			r.classSessions[i].Capacity = int32(capacity)
+			return r.classSessions[i], nil
+		}
+	}
+	return ClassSessionRecord{}, pgx.ErrNoRows
+}
+
 func (r *MemoryRepository) ListClassSchedulesByTenant(_ context.Context, tenantID string) ([]ClassScheduleRecord, error) {
 	if tenantID != r.tenant.ID {
 		return nil, nil