Extract inline CSS/JS, add EJS templates with shared layout

- Extract CSS into public/css/{shared,players,courses}.css
- Extract JS into public/js/{chart,tooltips,progress,players,courses}.js
- Consolidate 5 duplicated tooltip blocks into setupTooltip() helper
- Add EJS view engine with layout partial and nav partial
- Convert HTML pages to EJS templates (index.ejs, courses.ejs)
- Add /courses route with redirect from /courses.html
- Remove old monolithic HTML files (1478 + 612 lines)

server.js

@@ -9,6 +9,8 @@ const pageRoutes = require('./src/routes/pages');
 const app = express();
 const PORT = 3000;
 
+app.set('view engine', 'ejs');
+app.set('views', path.join(__dirname, 'views/pages'));
 app.use(express.static('public'));
 app.use(express.json());