Refactor: split server.js monolith into modular architecture

Extract 3410-line server.js into 12 focused modules:
- src/db.js: database init and migrations
- src/models/{player,course}.js: DB helper functions
- src/scrapers/{browser,player-http,player-puppeteer,course-puppeteer}.js
- src/services/{player-service,rating-calculator}.js
- src/routes/{players,courses,pages}.js

Remove dead code: duplicate saveRatingHistoryToDB, legacy
getPlayerCompetitionRatings/getPredictedRating/getAllRatingsWithScraping,
unused getCourseFromDB/getLatestOfficialRoundDate/testPDGARateLimit,
legacy cache Map, and POST /api/predicted-rating route.

Consolidate 5 duplicated Puppeteer launch blocks into launchBrowser().
server.js is now 28 lines: imports, middleware, mount routers, bootstrap.

src/models/course.js

@@ -0,0 +1,78 @@
+const { db } = require('../db');
+
+function saveCourseToDB(courseData) {
+  return new Promise((resolve, reject) => {
+    db.run(
+      `INSERT OR REPLACE INTO courses (name, link, city, last_updated)
+       VALUES (?, ?, ?, datetime('now'))`,
+      [courseData.name, courseData.link, courseData.city],
+      function(err) {
+        if (err) reject(err);
+        else resolve(this.lastID);
+      }
+    );
+  });
+}
+
+function getAllCoursesFromDB() {
+  return new Promise((resolve, reject) => {
+    db.all(
+      'SELECT * FROM courses ORDER BY name ASC',
+      [],
+      (err, rows) => {
+        if (err) reject(err);
+        else resolve(rows);
+      }
+    );
+  });
+}
+
+function saveLayoutToDB(courseId, layoutData) {
+  return new Promise((resolve, reject) => {
+    db.run(
+      `INSERT OR IGNORE INTO layouts (course_id, name, par)
+       VALUES (?, ?, ?)`,
+      [courseId, layoutData.name, layoutData.par],
+      function(err) {
+        if (err) reject(err);
+        else resolve(this.lastID);
+      }
+    );
+  });
+}
+
+function getLayoutsForCourse(courseId) {
+  return new Promise((resolve, reject) => {
+    db.all(
+      'SELECT * FROM layouts WHERE course_id = ? ORDER BY last_played DESC, name ASC',
+      [courseId],
+      (err, rows) => {
+        if (err) reject(err);
+        else resolve(rows);
+      }
+    );
+  });
+}
+
+function updateLayoutRating(courseId, layoutName, par, meanRating, ratingCount, lastPlayed = null) {
+  return new Promise((resolve, reject) => {
+    db.run(
+      `UPDATE layouts
+       SET mean_rating = ?, rating_count = ?, last_calculated = datetime('now'), last_played = ?
+       WHERE course_id = ? AND name = ? AND par = ?`,
+      [meanRating, ratingCount, lastPlayed, courseId, layoutName, par],
+      function(err) {
+        if (err) reject(err);
+        else resolve(this.changes);
+      }
+    );
+  });
+}
+
+module.exports = {
+  saveCourseToDB,
+  getAllCoursesFromDB,
+  saveLayoutToDB,
+  getLayoutsForCourse,
+  updateLayoutRating
+};