perf(parser): write the databases with 1 KiB pages

The browser fetches this file one page per HTTP request, so the page size
is the granularity of every read. At SQLite's 4 KiB default a row reached
by an index seek dragged 4 KB across the network; at 1 KiB it drags 1 KB.
A name search returns up to 100 scattered rows, so its row fetches fall
from about 400 KB to about 100 KB.

Measured on the rebuilt 2016 file: 6.3 rows share a page where 27 did.
The index walks are sequential and unaffected in bytes — the library's
read-ahead already collapses those into few requests.

Cost is 4% file size: 2016 288.6 -> 302.4 MB, 2017 237.7 -> 247.3 MB,
the site 528 -> 552 MB against the 1 GB GitHub Pages limit. Both
sql.js-httpvfs and sqlite-wasm-http recommend this page size.

The PRAGMA has to run before the DDL, since a page size is fixed once a
table exists, and requestChunkSize on the client has to match or every
page read spans two requests.

Row counts unchanged and through the assembler guards; query plans
re-checked and still index-driven on the rebuilt files.

parser/internal/writer/writer.go

@@ -43,6 +43,19 @@ func OpenDB(dbPath string) (*sql.DB, error) {
 	if err != nil {
 		return nil, fmt.Errorf("open db %s: %w", dbPath, err)
 	}
+	// Before the DDL, because a page size cannot change once a table exists —
+	// only the VACUUM in Finish could rewrite it, and only to this same value.
+	//
+	// 1 KiB rather than SQLite's 4 KiB default because the browser reads this
+	// file a page at a time over HTTP: a row fetched by index seek costs one
+	// page, so a search that returns 100 scattered rows transfers 100 KB
+	// instead of 400 KB. It costs about 5% file size, and both sql.js-httpvfs
+	// and sqlite-wasm-http recommend it. web/src/lib/sqlite.svelte.ts must
+	// request the same size.
+	if _, err := db.Exec("PRAGMA page_size = 1024"); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("set page size: %w", err)
+	}
 	if _, err := db.Exec(schema.DDL); err != nil {
 		db.Close()
 		return nil, fmt.Errorf("execute DDL: %w", err)