ci: Add GitHub Actions CI workflow

- Add basic CI pipeline for Rust project
- Build, test, format check, and clippy

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -0,0 +1,29 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+    branches: [ main, master ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Build
+      run: cargo build --verbose
+
+    - name: Run tests
+      run: cargo test --verbose
+
+    - name: Check formatting
+      run: cargo fmt -- --check
+
+    - name: Run clippy
+      run: cargo clippy -- -D warnings