Save path ./photos/YYYY/YYYY-MM/YYYY-MM-DD/YYYY-MM-DD.fileID.ext; download() from the cache first (closes #143)

Originals are saved at `{downloadDirectory}/YYYY/YYYY-MM/YYYY-MM-DD/YYYY-MM-DD.{fileID}{ext}`. The date is the photo's `takenAt` in local time, and `downloadDirectory` defaults to `./photos`, resolved when the library opens. The old `originals/` layout is gone.

`photo.download()` writes the original to `savePath`. It copies from the cache when the cache holds the original, and fetches otherwise. `lib.backup()` uses the same path and rule, and every album in `collections/` links to it. `isLocal` is true only when the original is at `savePath`.

For a file in several albums, one rule picks the copy everything uses: the most recently synced, with the lowest album ID breaking a tie.

Model: opus-5-5

src/library/store.ts

@@ -16,6 +16,7 @@ import { dirname } from "node:path";
 
 import { writeAtomic } from "../download/index.js";
 import type { Collection, EnteFile, Microseconds } from "../model/types.js";
+import { representative } from "./records.js";
 
 // Bumped only when the on-disk shape changes incompatibly. A file written
 // under a different version is discarded on load (see `load`): re-fetching
@@ -179,14 +180,16 @@ export class MetadataStore {
         return this.files.get(fileKey(collectionID, fileID));
     }
 
-    // Any membership of a file, or undefined. Every membership re-wraps the
-    // same underlying content key, so any one is enough to fetch the bytes;
-    // the content cache resolves a fileID to a file this way.
+    // The membership of a file its record is read from (`representative`), or
+    // undefined. Any membership could fetch the bytes, but the content cache
+    // resolves a fileID to a file this way so that it dates the save path
+    // from the same membership as `photo.savePath`.
     getFileByID(fileID: number): EnteFile | undefined {
+        const memberships: EnteFile[] = [];
         for (const file of this.files.values()) {
-            if (file.id === fileID) return file;
+            if (file.id === fileID) memberships.push(file);
         }
-        return undefined;
+        return memberships.length > 0 ? representative(memberships) : undefined;
     }
 
     listFiles(collectionID: number): EnteFile[] {