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
thumbnail pool with thumbnails.ensure. Originals: the pinned set — the
favorites album, then the latest-week window ending at the newest file —
through the content pool. The pinned set is the eviction predicate (#47), so 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. A cached file costs one map lookup and no fetch; each refresh re-kicks
the fills to pick up new files and retry failures. Progress via open()
onProgress and status() (thumbnailsCached/Total, originalsCached/Pinned).

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({