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.

tests/run.sh

@@ -8,9 +8,9 @@
 #
 # Locate the compiler via SX (overridable); defaults to the sibling sx repo.
 #
-# The vendored SQLite needs no flags here: src/db/sqlite.sx declares it
-# as a `#import c` unit, so `sx run` compiles (cached) and loads it as a
-# priority symbol target — the version assert in tests/sqlite_smoke.sx
+# SQLite needs no flags here: the sx library ships it (vendors/sqlite),
+# declared as a `#import c` unit — `sx run` compiles (cached) and loads it
+# as a priority symbol target; the version assert in tests/sqlite_smoke.sx
 # proves the OS copy never shadows it.
 set -u