fix(test): gstack-config-key-locale — suppress the skill_prefix auto-relink side effect

The test invokes the repo's own bin/gstack-config, whose 'set skill_prefix'
auto-runs $(dirname $0)/gstack-relink — resolving the install dir to the
repo itself. In any environment where the loop shares a working tree (the
free-tests CI container, a fresh-HOME run), gstack-patch-names rewrote all
52 tracked SKILL.md names to gstack- prefixed, poisoning five unrelated
suites downstream (hermetic-skills-seeding, host-config golden, skill-census,
skill-validation, spec-template-sync). GSTACK_SETUP_RUNNING=1 is the
documented suppression; relink behavior stays covered by relink.test.ts's
mock install.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/gstack-config-key-locale.test.ts

@@ -20,7 +20,14 @@ let stateRoot: string;
 function run(args: string[]) {
   const result = spawnSync(CONFIG, args, {
     encoding: "utf8",
-    env: { ...process.env, GSTACK_STATE_ROOT: stateRoot },
+    // GSTACK_SETUP_RUNNING suppresses `set skill_prefix`'s auto-relink side
+    // effect. Without it, this test invokes the REPO's gstack-config, whose
+    // auto-relink resolves the install dir from its own path — i.e. the repo —
+    // and gstack-patch-names rewrites all 52 tracked SKILL.md files to
+    // gstack-prefixed names, poisoning every downstream test that reads the
+    // live tree (observed in the free-tests CI job). Relink behavior itself is
+    // covered in isolation by test/relink.test.ts's mock install.
+    env: { ...process.env, GSTACK_STATE_ROOT: stateRoot, GSTACK_SETUP_RUNNING: "1" },
   });
 
   return {