feat: add CI/CD and release automation

- Add GitHub Actions CI for cross-platform testing (ubuntu/windows/macos × node 18/20/22)
- Add release workflow that auto-creates GitHub Releases and publishes to npm on tag push
- Add CONTRIBUTING.md with branching strategy (maintainers direct commit, contributors PR)
- Add MAINTAINERS.md with release workflows and recovery procedures
- Add PR template for contributors

Closes #221

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

.github/pull_request_template.md

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+## What
+
+<!-- One sentence: what does this PR do? -->
+
+## Why
+
+<!-- One sentence: why is this change needed? -->
+
+## Testing
+
+- [ ] Tested on macOS
+- [ ] Tested on Windows
+- [ ] Tested on Linux
+
+## Checklist
+
+- [ ] Follows GSD style (no enterprise patterns, no filler)
+- [ ] Updates CHANGELOG.md for user-facing changes
+- [ ] No unnecessary dependencies added
+- [ ] Works on Windows (backslash paths tested)
+
+## Breaking Changes
+
+None

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        node-version: [18, 20, 22]
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build hooks
+        run: npm run build:hooks
+
+      - name: Run tests
+        run: |
+          if npm pkg get scripts.test | grep -q '"test"'; then
+            npm test
+          else
+            echo "No test script defined, skipping"
+          fi
+        shell: bash
+
+      - name: Verify installation
+        run: |
+          npm link
+          npx get-shit-done-cc --version
+        shell: bash
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run lint
+        run: |
+          if npm pkg get scripts.lint | grep -q '"lint"'; then
+            npm run lint
+          else
+            echo "No lint script defined, skipping"
+          fi

.github/workflows/release.yml

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+name: Release
+
+on:
+  push:
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+'
+      - '!v*-*'  # Exclude pre-release tags
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Extract version from tag
+        id: version
+        run: |
+          VERSION=${GITHUB_REF#refs/tags/v}
+          echo "VERSION=$VERSION" >> $GITHUB_OUTPUT
+          echo "Releasing version: $VERSION"
+
+      - name: Extract changelog section
+        id: changelog
+        run: |
+          VERSION="${{ steps.version.outputs.VERSION }}"
+          awk -v ver="$VERSION" '
+            /^## \[/ {
+              if (found) exit
+              if ($0 ~ "\\[" ver "\\]") found=1
+            }
+            found {print}
+          ' CHANGELOG.md > release_notes.md
+
+          if [ ! -s release_notes.md ]; then
+            echo "## v$VERSION" > release_notes.md
+            echo "" >> release_notes.md
+            echo "See [CHANGELOG.md](https://github.com/${{ github.repository }}/blob/main/CHANGELOG.md) for details." >> release_notes.md
+          fi
+
+          echo "Release notes:"
+          cat release_notes.md
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          body_path: release_notes.md
+          draft: false
+          prerelease: false
+          generate_release_notes: false
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  publish:
+    needs: release
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          registry-url: 'https://registry.npmjs.org'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run build:hooks
+
+      - name: Publish to npm
+        run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}