Plain-record library snapshot and change subscription (closes #43)

Adds a synchronous, key-free snapshot() returning LibrarySnapshot (one PhotoRecord per fileID, deduped, newest first) with edited-name/time precedence (pubMagicMetadata over basic metadata) in milliseconds, plus AlbumRecord (favorites identified by type). subscribe({onChange}) delivers LibraryChange (changed/removed albums and files, refreshedAt) only when a refresh changes something; unsubscribe stops delivery. Built on the existing refresh loop; served from RAM, safe to send over IPC.

Model: opus-4-8

src/index.ts

@@ -42,6 +42,12 @@ export {
     type RefreshEvent,
     type RefreshProgressCallback,
 } from "./library/index.js";
+export type {
+    AlbumRecord,
+    PhotoRecord,
+    LibrarySnapshot,
+    LibraryChange,
+} from "./library/records.js";
 export { decryptCollection, decryptFile } from "./model/index.js";
 export { downloadFile, downloadThumbnail } from "./download/index.js";
 export type {