Add GitHub Actions workflows for build and deployment

- Add build.yml: builds Hugo site on all non-main branches and PRs
- Add deploy.yml: builds and deploys to S3 + CloudFront on main branch pushes
- Uses generic OIDC role for AWS authentication

.github/workflows/build.yml

@@ -0,0 +1,36 @@
+name: Build Site
+
+on:
+  push:
+    branches-ignore:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+          fetch-depth: 0
+      
+      - name: Setup Hugo
+        uses: peaceiris/actions-hugo@v3
+        with:
+          hugo-version: 'latest'
+          extended: true
+      
+      - name: Build Hugo site
+        run: hugo --minify
+      
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: hugo-build
+          path: public/
+          retention-days: 7