feat(email): per-weekday business hours + manual queue flush

Move the scheduled-email business-hours floor onto the business profile
as Google-style per-weekday opening blocks (multiple blocks/day for lunch
breaks). Migration 114 adds business_profile.business_hours (JSON) +
scheduled_email_floor_enabled; emailProcessor snaps a queued email to the
next open block, read in the profile timezone. Editor lives under
Settings → Business profile.
Add an admin "Send queued emails now" flush (POST /admin/email/flush-queue)
that drains the queue immediately, ignoring the business-hours floor — the
escape hatch before maintenance/updates. processEmailQueue now takes
{ignoreSchedule, limit} and returns send counts; the scheduled interval
run is unchanged.

frontend/src/services/email.service.ts

@@ -74,6 +74,16 @@ export const emailService = {
     await api.post('/admin/email/test', { test_email: testEmail });
   },
 
+  /** Flush the email queue immediately. Sends every pending email now,
+   *  bypassing the business-hours floor — the escape hatch for draining
+   *  the queue before maintenance/updates. */
+  async flushQueue(): Promise<{ processed: number; sent: number; failed: number }> {
+    const response = await api.post<{ processed: number; sent: number; failed: number }>(
+      '/admin/email/flush-queue'
+    );
+    return response.data;
+  },
+
   // Get all email templates
   async getTemplates(): Promise<EmailTemplate[]> {
     const response = await api.get<EmailTemplate[]>('/admin/email/templates');