Rewrite the README API reference for the shipped library surface (closes #53)

Replace the stale, disclaimer-topped API reference with one that matches the
cache/API library on `next`, and fix the Getting Started library snippet and
CLI-surface prose that the library rewrite left wrong. Documents `Library.open`
and its options (XDG cache default, refresh interval, precache, cache bounds,
pools), the default-read vs `fresh()` distinction and that the CLI's read
commands are fresh, the record types with `snapshot()`/`subscribe()`, the
`albums`/`photos`/`timeline` read surface, `Photo` content methods,
`thumbnails.ensure`, the `mldata` search surface, `backup()`, the three request
pools (10/5/25), and the on-disk cache layout. Notes the deferred content-hash
integrity check (issue #68). Also this is issue #13.

Docs-only: no code changed. Every documented signature was verified against the
source on `next`.

Model: opus-4-8

TODO.md

@@ -14,10 +14,19 @@ pre-1.0
 
 # Next Step
 
-Update the README API reference section to match the current implementation.
+Tag v1.0.0.
 
 # Completed Steps
 
+- 2026-09-22: Rewrote the README API reference (and the Getting Started / usage
+  snippets) to match the shipped cache/API library on `next` (issue 53, issue
+  13). Documented `Library.open` and its options, the default-read vs `fresh()`
+  distinction (and that the CLI's read commands are fresh), the record types and
+  `snapshot()`/`subscribe()`, the `albums`/`photos`/`timeline` read surface,
+  `Photo` content methods, `thumbnails.ensure`, the `mldata` search surface,
+  `backup()`, the three request pools (10/5/25), and the on-disk cache layout;
+  noted the deferred content-hash integrity check (issue 68). Docs-only; no code
+  changed.
 - 2026-09-22: Added resumable, deletion-aware enumeration to `Client` (issue 38,
   closes issue 7). `collectionsSince`/`filesSince` take a starting cursor,
   decrypt live records, surface tombstoned ids in a separate `deleted` list (a
@@ -122,7 +131,6 @@ Update the README API reference section to match the current implementation.
 
 # Future Steps
 
-- Tag v1.0.0.
 - Future desktop client, separate repo:
     - Electron app skeleton consuming this library.
     - Local SQLite cache keyed on (collectionID, fileID, updationTime).