chore: remove duplicate Excel files, add md5 audit script

- Drop 10_LamDong_GNFT (1) and 2.BacKan_YQNX(1): identical row content to
  siblings (Excel metadata differs but file size & sheet rows match)
- Add scripts/check-duplicates.js to detect byte-identical and row-identical
  files across data/raw and data/raw/update

scripts/check-duplicates.js

@@ -0,0 +1,29 @@
+// One-off audit: detect content-identical Excel files via md5
+import crypto from "crypto";
+import fs from "fs";
+import path from "path";
+
+const dirs = [
+  "D:/tiennm99/thptqg2017/data/raw",
+  "D:/tiennm99/thptqg2017/data/raw/update",
+];
+
+const byHash = {};
+for (const d of dirs) {
+  for (const f of fs.readdirSync(d)) {
+    const full = path.join(d, f);
+    if (!fs.statSync(full).isFile() || !f.endsWith(".xlsx")) continue;
+    const h = crypto.createHash("md5").update(fs.readFileSync(full)).digest("hex");
+    (byHash[h] ||= []).push(full);
+  }
+}
+
+const total = Object.values(byHash).reduce((s, a) => s + a.length, 0);
+const dupes = Object.entries(byHash).filter(([, a]) => a.length > 1);
+console.log(`Total files: ${total}`);
+console.log(`Unique by md5: ${Object.keys(byHash).length}`);
+console.log(`Duplicate groups: ${dupes.length}`);
+for (const [h, a] of dupes) {
+  console.log(`  ${h.slice(0, 12)}:`);
+  a.forEach((p) => console.log(`    ${p}`));
+}