test: raise timeouts for slow integration tests

Two test files were timing out at the default 5s on developer machines,
both pre-existing on origin/main but unrelated to this branch's bug fixes:

- test/gstack-artifacts-init.test.ts: 13 tests spawning real subprocesses
  via fake gh/glab/git shims in PATH. bun's fork+exec overhead pushed
  these past 5s consistently. Added a local test-wrapper that aliases
  test() with a 30s timeout (matches the brain-sync.test.ts pattern
  already in the repo).
- test/gstack-next-version.test.ts: one integration smoke test that
  spawns 'bun run ./bin/gstack-next-version' and parses the resulting
  JSON. The subprocess does a 'gh pr list' against the live GitHub API
  to enumerate claimed version slots. Network latency makes 5s tight;
  raised this single test to 30s.

No production code changed. The tests already passed deterministically
once given enough wall-clock time.

test/gstack-next-version.test.ts

@@ -153,6 +153,9 @@ describe("markActiveSiblings", () => {
 // Integration smoke — only runs if gh is available and authenticated. Confirms
 // the CLI executes end-to-end against real APIs without crashing.
 describe("integration (smoke)", () => {
+  // Bumps timeout to 30s — the test spawns a real `bun run` subprocess that
+  // does a `gh pr list` against the live GitHub API to inspect claimed slots.
+  // Network latency makes 5s tight on developer machines.
   test("CLI runs against real repo and emits parseable JSON", async () => {
     const proc = Bun.spawnSync([
       "bun",
@@ -178,5 +181,5 @@ describe("integration (smoke)", () => {
     expect(Array.isArray(parsed.claimed)).toBe(true);
     expect(parsed).toHaveProperty("siblings");
     expect(parsed.siblings).toEqual([]); // --workspace-root null disabled scanning
-  });
+  }, 30000);
 });