test(booking): freeze slot-mode contract before service-mode work

Adds SlotModeFrozenTest (#[Group('slot-mode-frozen')]) locking three things
against the multi-resource booking phase:
  - GET /api/v1/appointment-slots response shape
  - GET /api/v1/appointment-settings/month-availability/{uuid} response shape
  - public method signatures of SlotCalculatorService

Fixtures are structural, not raw snapshots: a fixed past date is rejected by
isWithinBookingWindow so an empty snapshot would prove nothing. Instead a
deterministic schedule on a computed near-future date, with epoch/uuid values
normalized to placeholders. What stays locked is the contract itself: keys,
ordering, types and local times.

No production code touched.

Task: docs/new_feture/taskes/task-00-service-mode-completion/
Slot-mode contract: unchanged (--group=slot-mode-frozen green, 3 tests)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/Appointment/fixtures/slot-mode-contract.json

@@ -0,0 +1,22 @@
+{
+  "_readme": "READ-ONLY — قرارداد منجمد GET /api/v1/appointment-slots. هیچ تسکی از فاز موتور چندمنبعی اجازهٔ به‌روزرسانی این فایل را ندارد. اگر SlotModeFrozenTest قرمز شد، کد باید برگردد نه این فایل. رجوع: docs/new_feture/taskes/_shared/red-lines.md",
+  "success": true,
+  "data": {
+    "doctor_uuid": "<uuid>",
+    "clinic_uuid": null,
+    "date": "<date>",
+    "sessions": [
+      {
+        "start_time": "09:00",
+        "end_time": "11:00",
+        "slots": [
+          { "start": "<epoch>", "end": "<epoch>", "start_time": "09:00", "end_time": "09:30", "location_id": 1, "is_available": true },
+          { "start": "<epoch>", "end": "<epoch>", "start_time": "09:30", "end_time": "10:00", "location_id": 1, "is_available": true },
+          { "start": "<epoch>", "end": "<epoch>", "start_time": "10:00", "end_time": "10:30", "location_id": 1, "is_available": true },
+          { "start": "<epoch>", "end": "<epoch>", "start_time": "10:30", "end_time": "11:00", "location_id": 1, "is_available": true }
+        ]
+      }
+    ],
+    "empty_reason": null
+  }
+}