fix: 9 test files import from dist/ instead of src/

[michaeldistel]

9 test files import from ../../dist/... — fail without a prior npm run build.

Files:

• tests/backend/test-main-gen.test.ts
• tests/backend/codegen-control-flow.test.ts
• tests/backend/codegen-composite.test.ts
• tests/backend/codegen-dynamic-memory.test.ts
• tests/backend/codegen-fb.test.ts
• tests/backend/codegen-oop.test.ts
• tests/backend/codegen-vla.test.ts
• tests/library/codesys-import.test.ts
• tests/cli/cli-library.test.ts

Fix: replace dist/ with src/ in all import paths.

Why src/ works: vitest uses Vite's native TypeScript pipeline (via vite.config.ts) to transpile .ts files on-the-fly at test time — no compiled dist/ output is needed or used. The vitest config already sets include: ["src/**/*.ts"] for coverage, confirming src/ is the canonical source. Importing from dist/ means tests silently test stale compiled output rather than current source.