Precache all thumbnails and pinned originals from Library.open (closes #48)

Two background fills start inside open() with no caller input, through the
shared pools (#45) at background priority, so on-demand work always preempts
them. Thumbnails: every file newest first until all are on disk, sharing the
pool with thumbnails.ensure. Originals: the pinned set — favorites, then the
latest-week window ending at the newest file — through the content pool. The
pinned set is the eviction predicate (#47): a pinned original is never evicted,
and a file that leaves the set (favorite removed, or window moved on a later
refresh) becomes an ordinary evictable original. Each refresh re-kicks the
fills to pick up new files and retry failures. Progress via open() onProgress
and status().

Model: opus-4-8

test/library/content-library.test.ts

@@ -99,6 +99,10 @@ describe("Library content wiring", () => {
             cacheDirectory: join(root, "cache"),
             contentSource: source,
             refreshIntervalSeconds: 3600,
+            // On-demand wiring only; the background precache (#48) is covered
+            // in precache.test.ts and would race the exact-count assertions.
+            precacheThumbnails: false,
+            precacheOriginals: false,
         });
 
         const photo = lib.photos.byID({ fileID: 1 });
@@ -122,6 +126,10 @@ describe("Library content wiring", () => {
             cacheDirectory: join(root, "cache"),
             contentSource: source,
             refreshIntervalSeconds: 3600,
+            // On-demand wiring only; the background precache (#48) is covered
+            // in precache.test.ts and would race the exact-count assertions.
+            precacheThumbnails: false,
+            precacheOriginals: false,
         });
 
         const results = await lib.thumbnails.ensure({