fix(modelscope): identify a model file by hash before filename

A file was matched to its published version by comparing basenames against
each version's `stats.fileList`.  Renaming the weights — routine once a
model is filed away, and the reason the scanner records a sha256 at all —
made the match fail silently, so the file lost its example images and its
preview with no indication why.

The detail payload's `ModelInfos.safetensor.files[]` carries a real sha256
per published file, and the local hash is already on disk, so match on that
first: it is the one identifier a rename cannot invalidate.  Exact basename
and `showName` matching remain as fallbacks, and an unknown hash falls
through to them rather than giving up, so a re-encoded file still resolves.

Verified against the live repository: a renamed `c1-st1000` file with its
hash yields the c1-st1000 image, the same rename without a hash yields
nothing, and supplying c1-st2000's hash resolves to the c1-st2000 image even
when the filename claims otherwise.

py/services/agent/agent_service.py

@@ -474,9 +474,13 @@ class AgentService:
                 cache.readmes[cache_key] = readme
 
         # Sites such as ModelScope keep part of the model card outside the
-        # README (author summary, curated tags, per-file example images).
+        # README (author summary, curated tags, per-file example images).  The
+        # recorded hash identifies the file even after the user renames it.
         card_context = await source.fetch_model_card_context(
-            ref.source_id, os.path.basename(model_path), cache=cache,
+            ref.source_id,
+            os.path.basename(model_path),
+            sha256=(metadata.get("sha256") or "").strip(),
+            cache=cache,
         )
         variables["source_description"] = card_context.description
         variables["source_base_model"] = card_context.base_model