refactor: collapse the two projects into one tree and move to npm

The repo held two near-duplicate projects. 2016/ and 2017/ each carried their
own React frontend, their own copy of the same Rust crate, and their own
package manager setup. 2016/tools/sync-from-thptqg2017.sh existed purely to
copy the parser source between them.

New layout:

  index.html + src/  the 2017 frontend, now the only one
  data/<id>/         2016, 2017, 2017-old, 2017-old2
  parser/            the single Rust crate, configs renamed to <id>.toml
  docs/              both projects' docs, 2016 copies suffixed -2016-legacy
                     pending the merge pass

<id> is now one identifier end to end: data/<id>/ feeds parser/configs/<id>.toml
and produces db/<id>.db.gz.

pnpm gives way to npm. pnpm-workspace.yaml existed only to whitelist
better-sqlite3's native build, which npm permits by default, so it has no
equivalent and is simply gone. Lockfiles cannot be converted; package-lock.json
is generated fresh. The migration direction is safe — pnpm's strict layout
forbids phantom dependencies, so anything that resolved under pnpm resolves
under npm's flat tree.

Adds parser/scripts/build-db.js and src/datasets.js: the four dataset IDs are
declared once and read by both the build tooling and (from the next phase) the
frontend.

Follow-on fixes the move made necessary:
  - eslint's Node-globals override pointed at scripts/, now parser/scripts/
  - crawl-baotintuc.js wrote to <root>/data, now data/2017
  - golden tests loaded configs by their old thptqg*-data.toml names

Drops the #[ignore]d Rust-vs-Node golden test. It shelled out to pnpm to run
scripts/build-database.js, a file removed when the parser was ported to Rust,
so it could never pass. check-duplicates.js and diff-datasets.js were already
broken before this change and are annotated as such rather than half-fixed.

63 Rust tests pass and clippy is clean from the new location.

index.html

@@ -1,26 +1,19 @@
 <!doctype html>
 <html lang="vi">
-<head>
-  <meta charset="utf-8">
-  <meta name="viewport" content="width=device-width, initial-scale=1">
-  <title>Tra cứu điểm thi THPT Quốc gia</title>
-  <style>
-    :root { color-scheme: light dark; }
-    body { font-family: system-ui, sans-serif; max-width: 42rem; margin: 3rem auto; padding: 0 1rem; line-height: 1.6; }
-    h1 { font-size: 1.5rem; }
-    li { margin: .5rem 0; }
-    .note { opacity: .7; font-size: .9rem; }
-  </style>
-</head>
-<body>
-  <h1>Tra cứu điểm thi THPT Quốc gia</h1>
-  <p>Tra cứu điểm thi tốt nghiệp THPT Quốc gia theo số báo danh — truy vấn SQL
-  chạy hoàn toàn trên trình duyệt (sql.js).</p>
-  <ul>
-    <li><a href="./2016/">Kỳ thi 2016</a> — 877.461 thí sinh</li>
-    <li><a href="./2017/">Kỳ thi 2017</a> — ~861.000 thí sinh</li>
-  </ul>
-  <p class="note">Phiên bản cũ của trang 2017: <a href="./2017/old/">old</a> ·
-  <a href="./2017/old2/">old2</a></p>
-</body>
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
+    <link
+      rel="stylesheet"
+      href="https://fonts.googleapis.com/css2?family=Be+Vietnam+Pro:wght@400;500;600;700&display=swap"
+    />
+    <title>Tra cứu điểm thi THPT QG 2017</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.jsx"></script>
+  </body>
 </html>