feat: appointment confirmation and cancellation (GH #98, GRO-153)

Add customer confirmation/cancellation flow for appointments:

- DB migration (0013): add confirmation_status, confirmed_at, cancelled_at,
  confirmation_token to appointments table with index on token column
- schema.ts + factories.ts + types: expose new columns and ConfirmationStatus type
- GET /api/book/confirm/:token — tokenized confirm via email link (redirects)
- GET /api/book/cancel/:token — tokenized cancel via email link, single-use token
- POST /api/appointments/:id/confirm — portal/staff confirm endpoint
- POST /api/appointments/:id/cancel — portal/staff cancel endpoint
- Reminder emails now include Confirm/Cancel CTA buttons with tokenized links
- Reminder service generates confirmation token if missing before sending
- Staff calendar shows confirmation status indicator on appointment cards
  and in the detail modal (confirmed ✓ / customer cancelled ✗)
- /booking/confirmed, /booking/cancelled, /booking/error redirect pages
- 23 new unit tests covering all new endpoints and edge cases

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/db/migrations/0013_appointment_confirmation.sql

@@ -0,0 +1,7 @@
+ALTER TABLE appointments
+  ADD COLUMN confirmation_status TEXT NOT NULL DEFAULT 'pending',
+  ADD COLUMN confirmed_at TIMESTAMPTZ,
+  ADD COLUMN cancelled_at TIMESTAMPTZ,
+  ADD COLUMN confirmation_token TEXT UNIQUE;
+
+CREATE INDEX idx_appointments_confirmation_token ON appointments (confirmation_token) WHERE confirmation_token IS NOT NULL;