feat(page): add typed keyset pagination for Bob (#15)

Add transport-neutral keyset pagination through native Bob query mods.
Preserve supported cursor value types in a compact versioned format, with
bidirectional pages, explicit row keys, and a separate opt-in count.
Include SQLite tests, PostgreSQL service CI, and the cursor-format ADR.

Closes #6

README.md

@@ -1,6 +1,6 @@
 # corestack go
 
-Shared Go building blocks. Includes `docs`, a checker for architecture decision records (ADRs) and implementation plans, and `lifecycle`, a service and worker coordinator.
+Shared Go building blocks. Includes `docs`, a checker for architecture decision records (ADRs) and implementation plans; `page`, Bob keyset pagination; and `lifecycle`, a service and worker coordinator.
 
 ## docs
 
@@ -20,6 +20,19 @@ docs check [--root DIR]                                # prints path:line: messa
 
 The format is specified in [docs/docs-format.md](docs/docs-format.md); that document is the complete rule set. Exit status is `0` when every record is valid, `1` when problems are reported and `2` for usage errors.
 
+## page
+
+[`page`](page/page.go) provides transport-neutral Bob keyset pagination with typed
+items, mixed-direction sorts, opaque typed cursors, and a separate opt-in count.
+Pass a trusted Sort and a typed row key in the same column order; sort columns
+must be non-null and end in a unique column. See the [runnable example](page/example_test.go)
+and [cursor decision](docs/adr/20261027T184351001Z-preserve-typed-sort-values-in-versioned-page-cursors.md).
+
+SQLite runs in-process in the normal test suite (requires CGO). PostgreSQL runs in
+CI; locally set `PAGE_POSTGRES_DSN` to an isolated test database to run the same
+flow. Set `PAGE_REQUIRE_POSTGRES=1` to fail rather than skip when the DSN is absent.
+MySQL mod composition compiles; its runtime behavior has not been verified.
+
 ## lifecycle
 
 `go.auvem.com/corestack/lifecycle` sets up modules in registration order, runs