security: isolate every gstack Bun entry point from the audited checkout's .env and bunfig.toml

Bun auto-loads .env, .env.local and .env.<NODE_ENV> from its cwd and runs a
cwd bunfig.toml preload before the program starts. gstack runs inside the repo
it audits, so a committed .env could steer state roots, the claude binary or
spend caps, and a bunfig preload ran arbitrary code in every bin and hook.

Every bun shebang, shell and skill caller, TypeScript spawn and compiled build
now disables both (--no-env-file --config=/dev/null, bunIsolationArgs(),
--no-compile-autoload-dotenv/bunfig), with a ratchet and hostile-fixture
regressions.

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

bin/gstack-code-intelligence

@@ -1,4 +1,4 @@
-#!/usr/bin/env bun
+#!/usr/bin/env -S bun --no-env-file --config=/dev/null
 /**
  * gstack-code-intelligence — pick a code-intelligence provider and use it to
  * index and search this repo. OPTIONAL: with nothing selected, gstack works