diigo-cache: SQL in .sql files, behind a read-only facet

No SQL text in the cache logic any more. Statements live in two files,
parsed by sqlStatements (`-- name:` sections, as in finquick's
brcal/gcbook.js) and imported as text (wrangler Text rule for *.sql):

- cache-read.sql: selects only, checked when the module loads
- cache-write.sql: schema, the v2 renumbering, etch, drops

store.ts turns them into two frozen facets with domain methods:
makeReader(sql) runs only the read statements (page, knownTotal,
deepestPageSince, pagesThrough); makeWriter(storage) only the write
ones (migrate, etch, dropPagesThrough), each change one transaction.

The cache migrates in its constructor under blockConcurrencyWhile, as
Cloudflare recommends, so readers never meet missing tables; the
migration test plants v1 storage and evicts to get a fresh activation.
A viewer() facet (PageViewer: stored pages and fill progress, from the
reader alone) is added for the public page.

Pure refactor: stored state and behavior unchanged.

Generated-by: Claude Opus 5.5

diigo-cache/src/cache-read.sql

@@ -0,0 +1,21 @@
+-- pageHeader:
+select total, etched_at from pages where page_num = ? and count = ?;
+
+-- pageItems:
+select items.json
+from page_members
+join items on items.item_id = page_members.item_id
+where page_members.page_num = ?
+order by page_members.pos;
+
+-- knownTotal:
+select total from pages where total > 0 order by etched_at desc limit 1;
+
+-- deepestPageSince:
+select max(page_members.page_num) as last
+from page_members
+join items on items.item_id = page_members.item_id
+where cast(items.updated as integer) >= ?;
+
+-- pagesThrough:
+select count(*) as n from pages where page_num <= ?;