feat: recurring appointments with cascading change propagation

Implements GitHub issue #9 — recurring appointment scheduling with
configurable frequency and cascade edit/cancel options.

Changes:
- DB: add `recurring_series` table (frequency_weeks) and series_id /
  series_index columns on appointments (migration 0003)
- API POST /appointments: accepts optional `recurrence` object
  (frequencyWeeks + count) that creates a full series in one transaction
- API PATCH /appointments/🆔 new `cascadeMode` field
  (this_only | this_and_future | all) applies time-delta shifts and
  field updates across the series
- API DELETE /appointments/🆔 new `?cascade=` query param cancels
  this_only / this_and_future / all series members
- Frontend: booking form gains a "Recurring appointment" checkbox with
  frequency and count pickers; calendar chips show a ↻ recurring label;
  detail modal shows "Recurring series" badge and a cascade-delete radio
  picker for series appointments

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

packages/db/migrations/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1773777600000,
       "tag": "0002_invoices",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "7",
+      "when": 1742169600000,
+      "tag": "0003_recurring_series",
+      "breakpoints": true
     }
   ]
 }