fix(ci): collect pytest tests and guard model-dependent ingestion

[Izzahsheikh]

Related issue

Fixes #156

Summary

The CI validation workflow previously used unittest discovery, which missed module-level pytest tests.

This PR switches CI to pytest and adds prerequisite checks for native-ingestion tests that require cached scene-model artifacts.

Changes

• Replace unittest discovery with pytest in the CI validation workflow
• Update PYTHONPATH to support imports from both src and the repository root
• Add cache-readiness checks for two model-dependent native-ingestion tests
• Preserve existing test assertions when the required model artifacts are available

Validation

• 819 passed, 0 failed, 10 skipped (local run with CI-equivalent dependency extras)
• 121 subtests passed
• Ruff checks passed
• git diff --check passed

All 10 skips have documented platform, tooling, or model prerequisites. No large AI models were downloaded.

The model-present native-ingestion path was not exercised locally because the required artifacts were unavailable.

[greptile-apps]

Heads up: Greptile reviewed this. Push back if it's wrong — it has no feelings.

Confidence Score: 5/5

[Medium impact] This PR appears safe to merge; no actionable issue was found in the workflow change or cache guards.

Summary

This PR makes CI run module-level pytest tests and skips two native-ingestion tests when scene-model weights are unavailable.

• CI runs its main test suite with pytest.
• Scene-indexing tests skip when SigLIP2 weights are missing.

_{Reviews (1) · Last reviewed commit: "fix(ci): collect pytest tests and guard ..." · Reviewed by Greptile}