fix: annotate let x = -1 with : number type

[cs01]

Summary

• 5 variables initialized to -1 were missing : number type annotations
• Native compiler can mistype these as integer instead of float, causing silent wrong behavior
• Files: parser-native/transformer.ts (2), semantic/type-assertion-checker.ts (2), codegen/expressions/access/member.ts (1)

Test plan

• All 436 tests pass
• verify:quick passes (tests + stage 0/1 self-hosting)