test: complete regex-escape class in worktree-safety assertion (#1589)

CodeQL alert #41 (js/incomplete-sanitization) flagged the partial
escape class /[-]/g at tests/worktree-safety.test.cjs:645 — it only
escaped hyphen-minus, leaving 13 other regex metacharacters (notably
backslash) unescaped. The canonical class /[.*+?^${}()|[\]\\]/g is
what every sibling escape in the test suite already uses
(bug-2839, bug-2760, 4-phase-complete, phase6-capstone-conformance).

Today dormant: the flag array is a hardcoded [a-z-] literal, so the
expanded class is a no-op for the four existing flags and the regexes
they produce are byte-identical. The fix prevents future drift — a
contributor adding e.g. '--output=file' would have silently introduced
a regex wildcard.

All 69 tests in the file pass. No user-facing behavior change.

Fixes #1589

tests/worktree-safety.test.cjs

@@ -642,7 +642,7 @@ describe('planWorktreeRecordAgent', () => {
     });
     assert.equal(plan.reason, 'missing_field');
     for (const flag of ['--agent-id', '--path', '--branch', '--base']) {
-      assert.match(plan.hint, new RegExp(flag.replace(/[-]/g, '\\$&')));
+      assert.match(plan.hint, new RegExp(flag.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')));
     }
   });