feat(builds): add canonical context identity

[jdchawla29]

Summary

• define one canonical build-context manifest for filesystem identity
• build deterministic deploy archives from that exact manifest and send it with build triggers
• replace the CLI source hash and Harbor truncated filesystem hashes with the canonical identity

Validation

• uv run --extra dev pytest hud/cli/utils/tests/test_context.py hud/cli/utils/tests/test_source.py hud/cli/tests/test_deploy.py hud/integrations/harbor/tests/test_contract.py hud/integrations/harbor/tests/test_integration.py -q (132 passed)
• focused Ruff checks passed
• focused ty checks passed