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.

docs/data-pipeline.md

@@ -181,6 +181,10 @@ silently drops 13,720 students** (Hanoi +7,275, HCM +6,445). That is what
 
 ## Expected row counts
 
+The databases are written with 1 KiB pages (`PRAGMA page_size` in
+`parser/internal/writer/writer.go`) because the browser fetches them a page per
+HTTP request. `CHUNK_BYTES` in `web/src/lib/sqlite.svelte.ts` must match.
+
 | id | Source rows | Skipped | DB rows |
 | --- | --- | --- | --- |
 | `2016` | 877,460 | 0 | **877,460** |