refactor: Replace generator with enhanced version

- Extracts full frontmatter metadata (originalDate, notion_*, authors, source)
- Correct date priority: frontmatter → filename → mtime → ctime
- All metadata exposed in index.json for frontend use

Phase 1 quick win complete.

.github/workflows/security.yml

@@ -0,0 +1,44 @@
+name: Security Scan
+
+on:
+  schedule:
+    - cron: 'weekly'
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  security:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        
+      - name: Run Trivy vulnerability scanner
+        uses: aquasecurity/trivy-action@master
+        with:
+          scan-type: 'fs'
+          scan-ref: '.'
+          severity: 'CRITICAL,HIGH'
+          format: 'sarif'
+          output: 'trivy-results.sarif'
+          
+      - name: Upload Trivy results
+        uses: github/codeql-action/upload-sarif@v2
+        if: always()
+        with:
+          sarif_file: 'trivy-results.sarif'
+          
+      - name: Create security issue on critical
+        if: failure() && github.event_name == 'schedule'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            github.rest.issues.create({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              title: '[Security] Critical vulnerabilities detected',
+              body: 'Trivy scan found critical vulnerabilities. Please review the security report.',
+              labels: ['security', 'critical']
+            })