Reorganize frontend into public/ with pages/ and js/ subdirectories

- public/index.html — landing page at root
- public/pages/ — all feature pages (regulations, loadboard, etc.)
- public/js/ — api.js, nav.js, mock data files
- All links updated to absolute paths (/pages/, /js/)
- Express static path updated to serve from public/
- Seed script path updated for new mock data location
- README updated with new project structure and setup guide
- Added .env.example template

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

server/.env.example

@@ -0,0 +1,7 @@
+# Environment variables for PilotEdge backend
+# Copy this to .env and fill in your values
+
+DATABASE_URL="postgresql://postgres:postgres@localhost:5432/pilotedge?schema=public"
+JWT_SECRET="change-this-to-a-long-random-string"
+PORT=3000
+NODE_ENV=development