Rename default booking source from WALKIN to DIRECT

docs/API_REFERENCE.txt

@@ -1551,7 +1551,7 @@ BOOKING APIS
   Request body (BookingCreateRequest):
 
   {
-    "source": "WALKIN",
+    "source": "DIRECT",
     "expectedCheckInAt": "2026-02-05T12:00:00+05:30",
     "expectedCheckOutAt": "2026-02-06T11:00:00+05:30"
   }

src/main/kotlin/com/android/trisolarisserver/controller/booking/BookingFlow.kt

@@ -145,7 +145,7 @@ class BookingFlow(
             property = property,
             primaryGuest = guest,
             status = BookingStatus.OPEN,
-            source = request.source?.trim().takeIf { !it.isNullOrBlank() } ?: "WALKIN",
+            source = request.source?.trim().takeIf { !it.isNullOrBlank() } ?: "DIRECT",
             checkinAt = null,
             expectedCheckinAt = expectedCheckInAt,
             expectedCheckoutAt = expectedCheckOutAt,

src/main/kotlin/com/android/trisolarisserver/models/booking/Booking.kt

@@ -32,7 +32,7 @@ class Booking(
     var status: BookingStatus = BookingStatus.OPEN,
 
     @Column(nullable = false)
-    var source: String = "WALKIN",     // WALKIN, WEBSITE, MMT, AGENT
+    var source: String = "DIRECT",     // DIRECT, WEBSITE, MMT, AGENT
 
     @Column(name = "source_booking_id")
     var sourceBookingId: String? = null,