test: linker harnesses source the skill-name helper

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

test/setup-playwright-best-effort.test.ts

@@ -653,6 +653,7 @@ function runLinker(opts: {
     '_print_windows_copy_note_once() { :; }',
     '_FOREIGN_SKIPPED_ENTRIES=()',
     extractFn('_link_or_copy'),
+    `. "${path.join(ROOT, 'bin/gstack-skill-name.sh')}"`,
     extractFn('_gstack_link_target_abs'),
     extractFn('_gstack_target_is_ours'),
     extractFn('_claude_entry_is_ours'),

test/user-render-out-dir-install.test.ts

@@ -190,6 +190,7 @@ describe('link_claude_skill_dirs prefers rendered SKILL.md (behavior)', () => {
         '_FOREIGN_SKIPPED_ENTRIES=()',
         '_BACKED_UP_SKILL_MDS=()',
         `_SKILL_BACKUP_ROOT="${os.tmpdir()}/gstack-harness-backups-${process.pid}"`,
+        `. "${path.join(ROOT, 'bin/gstack-skill-name.sh')}"`,
         extractFn(SETUP_SRC, 'link_claude_skill_dirs'),
         `link_claude_skill_dirs "${src}" "${skills}"`,
       ].join('\n');