ci: Add GitHub Actions workflows

- CI workflow for build, test, fmt, clippy
- Multi-platform builds (Linux, macOS x86_64, macOS ARM)
- Release workflow with artifact uploads
- Security audit integration

Note: Push with token that has 'workflow' scope

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

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

.github/workflows/ci.yml

@@ -0,0 +1,100 @@
+name: CI
+
+on:
+  push:
+    branches: [main, develop]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+  RUST_BACKTRACE: 1
+
+jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - name: Run cargo check
+        run: cargo check --all-targets --all-features
+
+  test:
+    name: Test Suite
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        rust: [stable]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+      - uses: Swatinem/rust-cache@v2
+      - name: Run tests
+        run: cargo test --all --verbose
+
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+      - name: Run rustfmt
+        run: cargo fmt --all -- --check
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy
+      - uses: Swatinem/rust-cache@v2
+      - name: Run clippy
+        run: cargo clippy --all-targets --all-features -- -D warnings
+
+  build-release:
+    name: Build Release
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        include:
+          - os: ubuntu-latest
+            target: x86_64-unknown-linux-gnu
+            artifact: miyabi-linux-x86_64
+          - os: macos-latest
+            target: x86_64-apple-darwin
+            artifact: miyabi-macos-x86_64
+          - os: macos-latest
+            target: aarch64-apple-darwin
+            artifact: miyabi-macos-aarch64
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: ${{ matrix.target }}
+      - uses: Swatinem/rust-cache@v2
+      - name: Build release binary
+        run: cargo build --release --target ${{ matrix.target }}
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: ${{ matrix.artifact }}
+          path: target/${{ matrix.target }}/release/miyabi*
+          if-no-files-found: ignore
+
+  security-audit:
+    name: Security Audit
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: rustsec/audit-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}