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/wrangler.tests.jsonc

@@ -6,7 +6,7 @@
 	"name": "diigo-cache-tests",
 	"main": "./tests/test-worker.ts",
 	"compatibility_date": "2026-09-29",
-	"rules": [{ "type": "Text", "globs": ["**/capnweb/dist/index.js"], "fallthrough": true }],
+	"rules": [{ "type": "Text", "globs": ["**/capnweb/dist/index.js", "**/*.sql"], "fallthrough": true }],
 	"services": [
 		{ "binding": "WEBAPP", "service": "fake-webapp", "entrypoint": "WebAppFactory" }
 	],