Add npm package age verification system

Problem: Need to ensure all npm packages are at least 2 weeks old before use

Solution:
- Created check-package-age.js script to verify package publish dates
- Added .npmrc to enforce exact version installation
- Created pin-old-versions.sh helper script
- Documented complete workflow in NPM-PACKAGE-AGE-POLICY.md

Usage:
  node scripts/check-package-age.js  # Verify all packages ≥ 2 weeks old
  npm ci                              # Install exact versions from lock file

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/.npmrc

@@ -0,0 +1,11 @@
+# Force exact version installation (no version range resolution)
+save-exact=true
+
+# Always use package-lock.json
+package-lock=true
+
+# Don't automatically update package-lock.json
+package-lock-only=false
+
+# Prevent automatic updates
+save-prefix=''