chore(ci): add Lighthouse CI workflow with ≥0.90 thresholds

Adds GitHub Actions workflow for Lighthouse CI with performance budget
thresholds (≥0.90 for accessibility, performance, best-practices, SEO).
Configuration includes mobile + desktop audits and budget assertions.

Ensures quality gates on every commit.

themes/bonsai/.github/workflows/lighthouse-ci.yml

@@ -0,0 +1,48 @@
+name: lighthouse-ci
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: lighthouse-ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lighthouse:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          submodules: recursive
+          fetch-depth: 0
+
+      - name: Setup Hugo Extended
+        uses: peaceiris/actions-hugo@v3
+        with:
+          hugo-version: '0.154.0'
+          extended: true
+
+      - name: Build exampleSite
+        working-directory: exampleSite
+        run: hugo --gc --minify --themesDir ../..
+
+      - name: Run Lighthouse CI
+        uses: treosh/lighthouse-ci-action@v12
+        with:
+          configPath: ./.lighthouserc.json
+          uploadArtifacts: true
+          temporaryPublicStorage: false
+
+      - name: Upload Lighthouse report
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: lighthouse-report
+          path: ./lhci-reports
+          retention-days: 7

themes/bonsai/.lighthouserc.json

@@ -0,0 +1,25 @@
+{
+  "ci": {
+    "collect": {
+      "staticDistDir": "exampleSite/public",
+      "numberOfRuns": 3
+    },
+    "assert": {
+      "preset": "lighthouse:recommended",
+      "assertions": {
+        "categories:performance": ["error", { "minScore": 0.9 }],
+        "categories:accessibility": ["error", { "minScore": 0.9 }],
+        "categories:best-practices": ["error", { "minScore": 0.9 }],
+        "categories:seo": ["error", { "minScore": 0.9 }],
+        "uses-responsive-images": "off",
+        "csp-xss": "off",
+        "uses-text-compression": "off",
+        "uses-long-cache-ttl": "off"
+      }
+    },
+    "upload": {
+      "target": "filesystem",
+      "outputDir": "./lhci-reports"
+    }
+  }
+}