refactor: optimize CI workflow triggers (#102)

Remove redundant push to master trigger from CI workflow since the
Release workflow already handles builds on master pushes.

Workflow strategy:
- CI: Runs on pull requests (validates before merge)
- Release: Runs on push to master (builds and creates releases)

This eliminates duplicate builds on master while maintaining full
test coverage on all changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jongear

.github/workflows/ci.yml

@@ -1,9 +1,6 @@
 name: CI
 
 on:
-  push:
-    branches:
-      - master
   pull_request:
     branches:
       - master