add test fixtures for switch, class extends, array/string methods, numeric enum

[cs01]

Summary

• Add 9 test fixtures covering previously untested features: switch statements (numeric + string), class inheritance, Array.from, Array.join, string replace/indexOf/slice, and numeric enums
• Switch tests are @test-skip — native parser transforms switch into independent if statements without else-chaining, so default case always runs. Fix requires transformer.ts changes that break self-hosting.

Test plan

• All 7 active tests pass with both JS and native compiler
• Switch tests skipped (known native parser bug documented)
• verify:quick passes including self-hosting Stage 1