fix: v0.5.1 — pull_image API (Image/pull_start, not Registry/pull_start)

The 0.5.0 prompt mis-attributed the API: pull_start lives on
SYNO.Docker.Image, not SYNO.Docker.Registry (live DSM capture).
search and tags ARE correctly on Registry; only pull_start belongs
to Image. Registry/pull_start returns "Method does not exist".

Parameters are unchanged (repository + tag both JSON-encoded), and
the Image/list polling for completion detection is untouched.

Tests updated to assert SYNO.Docker.Image/pull_start. CLAUDE.md
DSM-quirks section consolidates the Image vs. Registry split so
this trap is documented for future surface additions. References
#3 (already closed).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,21 @@
 
 All notable changes to this project will be documented in this file.
 
+## [0.5.1] - 2026-05-18
+
+### Fixed
+
+- `pull_image` (#3): the 0.5.0 implementation called
+  `SYNO.Docker.Registry/pull_start`, which DSM rejects with
+  "Method does not exist". A live DSM API capture confirmed that
+  `pull_start` actually lives on `SYNO.Docker.Image`, not
+  `SYNO.Docker.Registry`. The Registry API only exposes the
+  synchronous read-only methods (`search`, `tags`, `get/set/create/
+  delete`, `using`). Parameters are unchanged — both `repository`
+  and `tag` are still JSON-encoded — and the `Image/list` polling
+  for completion detection works as before. Note: #3 is already
+  closed; this is the follow-up fix.
+
 ## [0.5.0] - 2026-05-18
 
 ### Added