fix: add segmentHash to vector point payload and refactor tests

- Add segmentHash to payload in scanner.ts to fix vector point ID generation
- Split parser.spec.ts tests into focused unit tests (mocked dependencies)
- Move integration tests to new markdownIntegration.spec.ts file
- Each test suite now has clear, distinct responsibilities
- Fixes issue #4660: vector point ID collisions for large Markdown files

Author: MuriloFP