refactor: one directory per pipeline stage, and an assembler to drive them

The repository now reads as the pipeline it is: crawler fetches, parser
converts, assembler verifies and publishes, with data/ and web/ as the stores
they hand work through. go-parser is renamed parser now that there is no other.

The assembler replaces build-db.js and assemble-site.js. It compiles the
parser, builds and verifies each database, compresses it, runs the Vite build
and assembles _site — one command, and the only place that knows the order.

It also closes a real hole: nothing previously asserted that a database reached
the site. An empty staging directory assembled happily, so every page rendered,
every query 404d and CI stayed green. The row-count and size guards could not
catch that, since they only run when a database was built at all.

Removing Node from the root forced the dataset list out of web/src/datasets.js,
which the assembler cannot import. datasets.json is now the registry both sides
read — JSON because Go and the browser both parse it without a dependency —
while presentation stays in the web app, keyed by id and cross-checked against
the registry so a half-added dataset fails instead of half-working.

Guards verified by making each one fail: a missing database, and an expected
row count one higher than the truth.

parser/internal/sqlitedb/sqlitedb.go

@@ -0,0 +1,25 @@
+// Package sqlitedb registers the SQLite driver the parser writes with and names
+// it in one place.
+//
+// modernc.org/sqlite is a pure-Go SQLite, chosen so the whole module stays
+// cgo-free — grate, excelize and yaml.v3 are pure Go too, so CI can compile with
+// CGO_ENABLED=0 and no C toolchain.
+//
+// It is a machine-transpiled SQLite rather than the upstream C amalgamation that
+// Rust's rusqlite --bundled vendors (libsqlite3-sys 0.30.1). Two things make that
+// acceptable: this parser uses only plain SQL — no CTEs, window functions,
+// triggers or extensions — and the differential gate compares a full-table
+// SHA-256 plus PRAGMA table_info/index_list against live Rust output.
+//
+// Verified on linux/arm64 with v1.56.0 (SQLite 3.53.3): the full DDL including
+// the partial idx_ten_cum_thi index, INSERT OR REPLACE, and VACUUM.
+//
+// Fallback if the differential gate ever implicates the driver: mattn/go-sqlite3
+// is upstream C at the cost of cgo.
+package sqlitedb
+
+// Registers "sqlite" with database/sql.
+import _ "modernc.org/sqlite"
+
+// DriverName is the database/sql driver name to pass to sql.Open.
+const DriverName = "sqlite"