ci: run CI on release branches and all pull requests

The 1.0.0 work happens on a long-lived release/1.0.0 integration branch,
with one pull request per issue merged into it. The previous triggers
fired only for main, so those pull requests would have run no checks at
all and there would be nothing for the merge gate to check.

Push now covers release/**, and the pull_request branch filter is dropped
so every pull request is built regardless of its target.

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

Author: ausimian

.github/workflows/ci.yml

@@ -2,9 +2,10 @@ name: CI
 
 on:
   push:
-    branches: [ main ]
+    branches: [ main, 'release/**' ]
+  # No branch filter. A PR into a release integration branch has to get CI too,
+  # or there is nothing for the merge gate to check.
   pull_request:
-    branches: [ main ]
 
 jobs:
   precommit: