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)

src/routes/pages.js

@@ -1,13 +1,17 @@
 const express = require('express');
-const path = require('path');
 const router = express.Router();
 
 router.get('/', (req, res) => {
-  res.sendFile(path.join(__dirname, '../../index.html'));
+  res.render('index');
 });
 
+router.get('/courses', (req, res) => {
+  res.render('courses');
+});
+
+// Keep old URL working
 router.get('/courses.html', (req, res) => {
-  res.sendFile(path.join(__dirname, '../../courses.html'));
+  res.redirect('/courses');
 });
 
 module.exports = router;