fix(gbrain): DSNs percent-encode the password; body reads retry; stdout drains

Three codex-adversarial findings in the provision port: (1) raw DB_PASS
interpolation — a reserved character (/ # ? % @) restructured the URI,
provisioning succeeded, and every consumer then failed to parse the DSN
(unusable billable orphan); now encodeURIComponent, round-trip pinned.
(2) await res.text() sat outside the transport try — a server that sent
headers then reset the stream was an uncaught exit 1 instead of a
retry-then-exit-8. (3) The bin entrypoint called process.exit() after
unawaited stdout writes, truncating piped JSON; exitCode lets writes
drain.

bin/gstack-gbrain-supabase-provision

@@ -17,10 +17,13 @@
 
 import { runProvision } from '../lib/gbrain-supabase-provision';
 
+// exitCode, not process.exit(): exit() drops pending stdout writes, which
+// truncates piped JSON / large listings; setting exitCode lets writes drain
+// and the process exit naturally.
 runProvision(process.argv.slice(2)).then(
-  (code) => process.exit(code),
+  (code) => { process.exitCode = code; },
   (error) => {
     process.stderr.write(`gstack-gbrain-supabase-provision: ${(error as Error)?.stack ?? error}\n`);
-    process.exit(1);
+    process.exitCode = 1;
   },
 );