Add nostr backup constants and manifest models

src/nostr/backup_models.py

@@ -0,0 +1,26 @@
+from dataclasses import dataclass
+from typing import List, Optional
+
+# Event kind constants used for SeedPass backups
+KIND_MANIFEST = 30070
+KIND_SNAPSHOT_CHUNK = 30071
+KIND_DELTA = 30072
+
+
+@dataclass
+class ChunkMeta:
+    """Metadata for an individual snapshot chunk."""
+
+    id: str
+    size: int
+    hash: str
+
+
+@dataclass
+class Manifest:
+    """Structure of the backup manifest JSON."""
+
+    ver: int
+    algo: str
+    chunks: List[ChunkMeta]
+    delta_since: Optional[str] = None