test(desktop): the source hand-off fixture publishes stable as GitHub's latest release

158cd52a6b made the stable channel read only GitHub's latest published
release (releases/latest) and updated the Python fixtures, but the Desktop
electron fixture in checkout-source.test.ts still served stable only through
the R2 channel record and release-candidates pointer. Its stable leg now
returns release-unavailable ("No published stable release could be
verified"), so main's JS & TS checks job is red since 07908be267.

The fixture now serves /repos/NousResearch/hermes-agent/releases/latest for
the stable tag, the same route the Python fixtures added. No assertion changed.

apps/desktop/electron/updater/checkout-source.test.ts

@@ -266,6 +266,12 @@ it('carries each install channel from Python publication checks into the source
       responses.set(`/repos/NousResearch/hermes-agent/commits/${tags[channel]}`, { sha })
     }
 
+    // Stable is GitHub's latest published release; R2 holds no stable record.
+    responses.set('/repos/NousResearch/hermes-agent/releases/latest', {
+      tag_name: tags.stable,
+      draft: false,
+      prerelease: false
+    })
     responses.set('/releases/stable/release-candidates.json', { tag: tags.stable, commit: commits[1] })
     // The 'main' subscription is a source-branch channel record under the R2 protocol.
     responses.set(