Photo: save path, is-local, content bytes, metadata and EXIF getters (closes #141)

A Photo now has savePath and isLocal, which look only at the disk;
content() and exif(), which may download the original; and modifiedAt,
hash, fileSize and year. PhotoRecord gains modifiedAt, hash and fileSize.
The JPEG EXIF scan moves from metadata-backup.ts to the new src/exif.ts,
so the read surface does not import the backup command.

Model: opus-5-5

src/library/records.ts

@@ -5,10 +5,11 @@
 // owner ruling 5). The decrypted `Collection`/`EnteFile` objects stay in RAM in
 // the main process; the window only ever sees these records.
 //
-// Ente holds edited/basic times in microseconds; records expose `takenAt` in
-// milliseconds. The magic-metadata field names below are the ones the Ente
-// clients write, confirmed against the repo's own fixtures: `w`/`h` in
-// test/cli/metadata-backup.test.ts, `visibility` in test/library/store.test.ts.
+// Ente holds edited/basic times in microseconds; records expose `takenAt` and
+// `modifiedAt` in milliseconds. The magic-metadata field names below are the
+// ones the Ente clients write, confirmed against the repo's own fixtures:
+// `w`/`h` in test/cli/metadata-backup.test.ts, `visibility` in
+// test/library/store.test.ts.
 
 import type {
     Collection,
@@ -33,12 +34,19 @@ export interface PhotoRecord {
     // Milliseconds. `pubMagicMetadata.editedTime` when the user edited the
     // date, else basic-metadata `creationTime`.
     takenAt: number;
+    // Milliseconds. Basic-metadata `modificationTime`.
+    modifiedAt: number;
     fileType: FileType;
     caption?: string;
     width?: number;
     height?: number;
     latitude?: number;
     longitude?: number;
+    // The content hash the uploader recorded (`FileMetadata.hash`); files from
+    // very old clients have none.
+    hash?: string;
+    // The original's size in bytes, as the server reports it.
+    fileSize?: number;
     isArchived: boolean;
     isHidden: boolean;
     // Local cache paths, set once a later phase caches the bytes; unset here.
@@ -125,6 +133,7 @@ const toPhotoRecord = (
         albumIDs,
         title: asString(pub.editedName) ?? rep.metadata.title,
         takenAt: microsToMillis(takenAtMicros),
+        modifiedAt: microsToMillis(rep.metadata.modificationTime),
         fileType: rep.metadata.fileType,
         isArchived: visibility === VISIBILITY_ARCHIVED,
         isHidden: visibility === VISIBILITY_HIDDEN,
@@ -140,6 +149,8 @@ const toPhotoRecord = (
         record.latitude = rep.metadata.latitude;
     if (rep.metadata.longitude !== undefined)
         record.longitude = rep.metadata.longitude;
+    if (rep.metadata.hash !== undefined) record.hash = rep.metadata.hash;
+    if (rep.file.size !== undefined) record.fileSize = rep.file.size;
 
     return record;
 };