sqlite moves into the sx library: import vendors/sqlite/sqlite.sx

The amalgamation and the bindings now ship with sx itself
(sx library/vendors/sqlite/ — bindings + c/ amalgamation); every
import flips from ../src/db/sqlite.sx to vendors/sqlite/sqlite.sx,
resolved through the compiler's stdlib search paths. vendor/ and
src/db/ leave this repo entirely. make test 22/22 — the object cache
keys on content, not path, so the relocated source still hits the
existing cache entries.

Makefile

@@ -10,12 +10,13 @@ BUILD_DIR := build
 # product entry point. Further entry points under src/ get added here as
 # they land.
 #
-# The vendored SQLite (vendor/sqlite/) is part of the PROGRAM, not the
-# build system: src/db/sqlite.sx declares it as a named `#import c` unit
-# (pinned defines + -O2 + #source), so sx compiles and links it through
-# its content-addressed object cache (.sx-cache/) — once per checkout.
-# `sx build` links the unit's objects into the binary; `sx run` loads
-# them as a priority symbol target the OS libsqlite3 cannot shadow.
+# SQLite ships with sx itself (its library's vendors/sqlite module,
+# imported as `vendors/sqlite/sqlite.sx`): a named `#import c` unit the
+# compiler builds through its content-addressed object cache
+# (.sx-cache/) — once per machine. `sx build` links the unit's objects
+# into the binary; `sx run` loads them as a priority symbol target the
+# OS libsqlite3 cannot shadow. Nothing SQLite-related lives in this
+# repo anymore.
 SMOKE := tests/smoke.sx
 DIST  := src/dist.sx