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)

package.json

@@ -8,6 +8,7 @@
     "dev": "nodemon server.js"
   },
   "dependencies": {
+    "ejs": "^4.0.1",
     "express": "^4.18.2",
     "fs": "^0.0.1-security",
     "puppeteer": "^21.0.0",