Use the unified sanka CLI from the Python SDK

[sanka-change-bot]

Summary

Update SankaMigrate and AsyncSankaMigrate to invoke the consolidated sanka executable, retain the sanka-cli/v1 protocol and direct argv behavior, refresh developer guidance, and add an opt-in real-CLI acceptance lane.

Audit

• Requester: @hira29
• Authoring identity: Sanka Change Bot
• Head SHA: f7302644343b8aa236103f2c291808dfbc0e3ce6
• Risk: medium
• Deploy mode: none
• Production surface: PyPI sanka-sdk Python package (publication deferred)

Validation

• rtk env -u SANKA_CLI_EXECUTABLE uv run --frozen -- python -W error -m unittest discover -s tests -v -> passed
• rtk uv run --frozen -- ruff check . -> passed
• rtk uv build --out-dir /tmp/sanka-python-consolidation-pr -> passed
• Default suite passed with the real-CLI lane intentionally skipped; reviewed real-CLI suite previously passed 28/28. -> reported passed
• No-local-check reason: N/A
• Required GitHub checks must complete before landing.
• Valid review findings must be addressed before landing.

Change Safety

• Data or migration impact: No data migration, SDK publication, or external service change.
• Rollback: Revert the merge commit; the SDK can continue invoking the prior executable until the CLI cutover is released.
• Monitoring: GitHub checks and post-release real-executable acceptance against published sanka-cli.

Approval And Deployment Authorization

• The PR is ready for final human review; no intended code changes remain.
• The listed head SHA is the exact revision being presented for approval.

By approving this PR, the reviewer authorizes merge of the exact approved revision. This repository has no production deployment in this flow. A later push requires a new approval.