feat: build full CI pipeline

[HotFazz]

Labels: feat, P1, P2

Wire together the webhook handler → clone → compile → test into a single pipeline.

• If compilation fails, skip tests and report compilation failure
• If tests fail, report test failure
• If everything passes, report success
• Log each stage with timestamps

Acceptance criteria:

• End-to-end: push to GitHub → webhook → clone → compile → test → result logged
• Each stage's success/failure is independently tracked
• Integration test for the full pipeline