Security hardening: headers, scanning, Docker, firewall

- Caddy: HSTS, CSP, X-Frame-Options, nosniff, Referrer-Policy,
  Permissions-Policy on all responses
- Caddy: Block scanner paths (.env, .git, wp-config, etc.) with 403
- CI: Gitleaks secret scanning + pnpm audit for vulnerabilities
- Dependabot: Weekly npm + GitHub Actions + monthly Docker updates
- Docker: Non-root user in journal, planner, and brouter containers
- Server: UFW firewall (22/80/443 only) + fail2ban (8 IPs already banned)
- SECURITY.md: Vulnerability disclosure policy
- Privacy page: Security practices section added

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -11,6 +11,27 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  security:
+    name: Security Scan
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+      - name: Gitleaks
+        uses: gitleaks/gitleaks-action@v2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - uses: pnpm/action-setup@v4
+      - uses: actions/setup-node@v6
+        with:
+          node-version: 24
+          cache: pnpm
+      - run: pnpm install --frozen-lockfile
+      - name: Dependency audit
+        run: pnpm audit --audit-level=high
+        continue-on-error: true
+
   typecheck:
     name: Typecheck
     runs-on: ubuntu-latest