ci(local-model): name the digest contract and ask for measured rows first

A row can pin its build only as `digest`, the value /api/tags reports
after the pull, and LocalModelEntrySchema must gain that optional field
before the weekly check can compare it. The script header and the docs
now say so, so the field cannot arrive under another name and be ignored.

Until it exists, the report's digest table names the build a Mac pulls
for each row and asks for the rows with measured figures first: their
memory figures describe one build, and without a digest a rebuild of
about the same size goes unnoticed. A switch between the mlx and the gguf
build is still caught by the size check (2% or more apart).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/local-models.md

@@ -273,8 +273,12 @@ For every model row it checks:
 - **The build a Mac pulls runs on the pinned runtime**: its config declares no newer
   Ollama (`requires`) than `OLLAMA_RUNTIME_PIN`.
 - **The pinned digest**, once a row carries one: a Mac would still pull that manifest. The
-  catalogue pins none yet, so the report lists today's digests, the one to pin being what
-  `/api/tags` reports after the pull.
+  field is `digest` and its value is what `/api/tags` reports after the pull. The catalogue
+  schema does not have it yet: `LocalModelEntrySchema` must gain an optional `digest` under
+  exactly that name, or the check never compares it. Until then the report lists today's
+  digests, rows with measured figures first, because without a digest a rebuild of about the
+  same size goes unnoticed (a switch between the mlx and the gguf build does not: their sizes
+  differ by 2% or more).
 
 For the runtime pin it checks whether a newer Ollama release exists, and whether the pinned
 `ollama-darwin.tgz` is still on GitHub with the pinned size and sha256.