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.

docs/system-architecture.md

@@ -0,0 +1,97 @@
+# System Architecture
+
+Static site. No backend. Browser downloads a compressed SQLite file at boot, then every query runs locally via `sql.js` (WASM).
+
+## Data flow
+
+```
+Excel files (.xls / .xlsx)
+        │
+        ▼  build-database*.js (Node)
+SQLite DB (public*/thptqg2017.db)
+        │
+        ▼  gzip -9
+thptqg2017.db.gz (~47 MB for main variant)
+        │
+        ▼  Vite build copies public*/ into dist/
+Static site on GitHub Pages
+        │
+        ▼  browser loads
+sql.js (WASM) opens the .db → queries run client-side
+```
+
+## Three deployment variants
+
+One repo → three independent sites, same frontend, different dataset.
+
+| Variant | Route | Source dir | Public dir | Build cmd |
+|---|---|---|---|---|
+| main  | `/thptqg2017/`      | `data/`      | `public/`      | `npm run build` |
+| old   | `/thptqg2017/old/`  | `data-old/`  | `public-old/`  | `npm run build:old` |
+| old2  | `/thptqg2017/old2/` | `data-old2/` | `public-old2/` | `npm run build:old2` |
+
+`vite.config.js` reads `process.env.VARIANT` and switches `base`, `publicDir`, `outDir` accordingly. `emptyOutDir` is on only for the main build so the variant builds merge into `dist/old/`, `dist/old2/` cleanly.
+
+## Schema (all 3 DBs share this)
+
+```sql
+CREATE TABLE student (
+  so_bao_danh   TEXT PRIMARY KEY,     -- exam ID (8 digits, first 2 = province)
+  ho_ten        TEXT NOT NULL,
+  ho_ten_ascii  TEXT NOT NULL,        -- NFD-stripped lowercase for accent-insensitive search
+  ngay_sinh     TEXT,                 -- dd/mm/yyyy
+  toan, ngu_van, vat_ly, hoa_hoc, sinh_hoc, khtn,
+  lich_su, dia_ly, gdcd, khxh,
+  tieng_anh, tieng_phap, tieng_nga, tieng_trung   REAL
+);
+CREATE INDEX idx_ho_ten        ON student(ho_ten);
+CREATE INDEX idx_ho_ten_ascii  ON student(ho_ten_ascii);
+```
+
+No German / Japanese language columns — neither appears in any source file.
+
+Each score column is `NULL` when the student didn't take that subject. A student's "admission block" total is only computed when all 3 required subjects are non-null.
+
+## Parse quirks (why 3 builder scripts)
+
+Each dataset had a different quirk. Rather than one mega-parser with mode flags, each builder script is ~70 lines and isolates its own workarounds.
+
+| Dataset | Quirk | Mitigation |
+|---|---|---|
+| data/ (baotintuc .xls) | Hanoi + HCM overflow past the 65,536 row-per-sheet .xls limit | Iterate all `wb.SheetNames` |
+| data-old/ (xlsx) | Single-sheet always; one bogus header row (`SOBAODANH`/`HO_TEN`) leaked into an earlier DB | Strict numeric-SBD guard rejects the leak |
+| data-old2/ (xlsx) | HCM overflow + many blank trailing rows | Multi-sheet walk + blank-row pre-filter |
+
+Shared concerns (regex, schema, `toAscii`, header detection) live in `scripts/build-lib.js`.
+
+## Admission blocks
+
+Vietnamese universities admit students based on 3-subject combinations called "admission blocks" (khối thi). `src/lib/admission-blocks.js` lists all 49 official 2017 blocks computable from our schema (A00–A11, B00–B08, C00–C20, D01–D15). Each entry is `{ code, subjects: [3 keys], label }`.
+
+`computeBlocks(student)` returns only blocks where the student has all 3 subject scores, sorted by total desc. Used by the student detail card.
+
+The SQL preset "Top 10 best-block in Long An" materialises all 49 blocks as a `UNION ALL` CTE, picks each student's best block via `ROW_NUMBER() OVER (PARTITION BY so_bao_danh ORDER BY s DESC, k)`, then ranks across students.
+
+## Score tiers (UI coding)
+
+6-level TFT rarity ladder (white → green → blue → purple → gold → prismatic). Defined in `scoreTier()` in `src/lib/admission-blocks.js`.
+
+| Tier | Range | UI label (Vietnamese) | English |
+|---|---|---|---|
+| common    | ≤ 1   | Điểm liệt  | Disqualifying |
+| uncommon  | < 5   | Chưa đạt   | Below passing |
+| rare      | 5–6.5 | Trung bình | Average |
+| epic      | 6.5–8 | Khá        | Good |
+| legendary | 8–9   | Giỏi       | Very good |
+| prismatic | 9–10  | Xuất sắc   | Excellent |
+
+Color + icon + text label — never color-only.
+
+## Frontend key behaviors
+
+- Query state lives in `App.jsx` and is synced to URL `?q=...` via `history.replaceState` — bookmarkable, shareable.
+- `SearchForm` is a controlled component that 300ms-debounces input changes and auto-triggers search once the query is long enough (3+ digits for SBD, 2+ chars for name).
+- Detection: all-digits → exact `so_bao_danh` match; ASCII-only → folded `ho_ten_ascii LIKE`; has Vietnamese diacritics → search both `ho_ten` and folded column.
+- Exactly 1 result → `StudentDetail` card; 0 or >1 → `ScoreTable`.
+- Global `/` key focuses the search input when not already typing.
+- Share button on the detail card uses Web Share API when present, else clipboard with a pre-formatted summary + deep-link URL.