Update GitHub Actions workflow with concurrency controls and run-name

- Add run-name with actor information for better visibility
- Add concurrency group to cancel duplicate runs
- Improve CI efficiency by preventing redundant builds

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

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

Author: will-molloy

.github/workflows/build.yml

@@ -1,10 +1,15 @@
 name: build
+run-name: build by @${{ github.actor }}
 
 on:
   pull_request:
   push:
     branches: [ main ]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: ${{ matrix.os }}