feat(backup): add BACKUP and RESTORE_REQUESTS collection constants to FirestoreCollections

app/src/main/java/app/closer/data/remote/FirestoreCollections.kt

@@ -41,6 +41,18 @@ object FirestoreCollections {
         const val WHEEL = "wheel"
         const val DESIRE_SYNC = "desire_sync"
         const val HOW_WELL = "how_well"
+
+        // E2EE conversation backup (couple-key encrypted) + full partner-assisted restore.
+        const val BACKUP = "backup"
+        const val RESTORE_REQUESTS = "restore_requests"
+    }
+
+    // ── Docs/subcollections under couples/{coupleId}/backup ───────────────────
+    object Backup {
+        /** Fixed manifest doc: pointers + generation for optimistic concurrency. */
+        const val MANIFEST_ID = "manifest"
+        /** Incremental encrypted chunk docs appended since the last cursor. */
+        const val CHUNKS = "chunks"
     }
 
     // Standalone subcollection name that appears under both couples/{id} and users/{uid}