Add fresh read variants that await a server round-trip (closes #75)

Owner amendment to design #36: alongside the default reads, which answer
from RAM and refresh in the background, `Library.fresh()` forces a refresh,
awaits it, and only then hands back the albums/photos/timeline namespaces, so
a caller (the CLI, in #52) gets server-current data.

The background loop and the default reads are unchanged. Both paths now share
one in-flight-cycle slot: the loop skips when a cycle runs and swallows its
errors as before; a fresh read coalesces onto that cycle or starts one, and
propagates a failure so a refresh that could not complete rejects the caller
instead of silently serving stale data. Concurrent fresh reads therefore
collapse to a single server round-trip.

Model: opus-4-8

src/library/read.ts

@@ -193,6 +193,15 @@ export interface TimelineAPI {
     groups(args: { groupBy: GroupBy; filter?: PhotoFilter }): TimelineGroup[];
 }
 
+// The surface `Library.fresh()` resolves to (issue #75). It is the same three
+// read namespaces as the default `albums`/`photos`/`timeline`, handed back only
+// after a forced refresh has brought the local copy current.
+export interface FreshReads {
+    albums: AlbumsAPI;
+    photos: PhotosAPI;
+    timeline: TimelineAPI;
+}
+
 export const makeAlbumsAPI = (
     derive: () => DerivedRecords,
     content?: PhotoContent,