fix: declare destructured for-of variables in semantic analyzer + map iteration tests

[cs01]

Summary

• Bug fix: for (const [k, v] of map.entries()) previously failed with "Reference to undeclared variable" because the semantic analyzer only declared single-variable for-of loops (variableName), not destructured ones (destructuredNames). Now both paths are handled.
• New tests: 5 test fixtures covering Map iteration patterns that were previously untested:
  • map-entries.ts — for...of map.entries() with string keys/values
  • map-entries-bare.ts — for...of map (bare map iteration)
  • map-keys.ts — map.keys() iteration
  • map-values.ts — map.values() iteration
  • map-string-number-entries.ts — Map<string, number> entries iteration

Test plan

• All 458 tests pass
• npm run verify:quick (in progress)