Decrypt and persist all file metadata layers

Extends RawEnteFile and EnteFile with optional magicMetadata and
pubMagicMetadata fields. Both are secretstream blobs under the file
key, decrypted to arbitrary JSON (Record<string, unknown>).

pubMagicMetadata carries ML-derived data from the Ente clients:
camera make/model, image dimensions, datetime with timezone offset,
and (when present) captions, editedName, face labels, keywords.

magicMetadata carries private mutable fields like visibility.

Backup now writes per-file JSON at originals/<fileID>.json containing
all three metadata layers (basic + magic + pubMagic).

Live-tested: all 11 files in the dev account have pubMagicMetadata
with SONY DSC-RX1RM3 camera info and 3000x2000 dimensions.

src/model/types.ts

@@ -40,6 +40,8 @@ export interface EnteFile {
     ownerID: number;
     key: Uint8Array;
     metadata: FileMetadata;
+    magicMetadata?: Record<string, unknown>;
+    pubMagicMetadata?: Record<string, unknown>;
     file: FileBlob;
     thumbnail: FileBlob;
     updationTime: Microseconds;
@@ -59,6 +61,13 @@ export interface RawCollection {
     isDeleted?: boolean;
 }
 
+export interface RawMagicMetadata {
+    version: number;
+    count: number;
+    data: string;
+    header: string;
+}
+
 export interface RawEnteFile {
     id: number;
     collectionID: number;
@@ -66,6 +75,8 @@ export interface RawEnteFile {
     encryptedKey: string;
     keyDecryptionNonce: string;
     metadata: { encryptedData: string; decryptionHeader: string };
+    magicMetadata?: RawMagicMetadata;
+    pubMagicMetadata?: RawMagicMetadata;
     info?: { fileSize?: number; thumbSize?: number };
     file: { decryptionHeader: string };
     thumbnail: { decryptionHeader: string };