ci: run on push to main only to avoid duplicate PR runs

A push to a claude/** branch with an open PR triggered both the push
and pull_request events. The concurrency group keys on github.ref,
which differs between the two (refs/heads/... vs refs/pull/N/merge),
so neither run was cancelled and the whole pipeline (including E2E)
ran twice. Drop claude/** from the push trigger; branch work is now
validated once via the pull_request event.

.github/workflows/ci.yml

@@ -2,7 +2,7 @@ name: CI
 
 on:
   push:
-    branches: [main, 'claude/**']
+    branches: [main]
   pull_request:
     branches: [main]
   workflow_call: