refactor(parser): remove the Rust crate now that Go is at parity

The Go parser has matched the Rust one field-by-field across all four datasets,
so the Rust crate is retired and CI builds the Go binary instead.

crawl-baotintuc.js moves to go-parser/scripts/ — it is the only mechanism for
refreshing data/2017 and has a documented runbook. check-duplicates.js and
diff-datasets.js are dropped: both had been broken since before the repo was
unified, and neither had a caller. db-stats.js and verify-parity.js are dropped
as superseded by differential-parity.mjs, which compares more and cannot
silently skip a dataset.

The reader-fidelity oracle is kept and marked frozen. It was produced by the
Rust reader so it can no longer be regenerated, but it still fails if any single
cell of any of the 299 input files reads differently.

Source comments cite the original Rust by file and line; those paths resolve at
tag pre-go-parser-removal, recorded in go-parser/README.md.

docs/system-architecture.md

@@ -31,7 +31,7 @@ data/<id>/*.xls(x)
 One identifier ties the whole pipeline together:
 
 ```
-data/2017-old/  →  parser/configs/2017-old.yml  →  db/2017-old.db.gz  →  /thptqg/2017-old/
+data/2017-old/  →  go-parser/configs/2017-old.yml  →  db/2017-old.db.gz  →  /thptqg/2017-old/
 ```
 
 `src/datasets.js` declares the four ids once. The frontend, the database build