fix(ci): unset XDG_CONFIG_HOME for npm installer smoke test

The smoke test creates temp home directories with .config/kimchi markers
for agent detection. On Linux CI runners XDG_CONFIG_HOME may point to the
runner's real config path, causing resolvedAgentTargets to look outside
the temp home. Unset it so detection resolves against the test's temp dir.

.github/workflows/ci.yml

@@ -514,6 +514,8 @@ jobs:
 
       - name: Test npm installer smoke (prune, backup, publish)
         if: steps.classify.outputs.changelog_only != 'true' && steps.classify.outputs.docs_only != 'true'
+        env:
+          XDG_CONFIG_HOME: ""
         run: node test/scripts/install_js_smoke.mjs
 
   test-focused: