release: Python SDK 0.7.103 parity

[RobLe3]

Summary

• publish the already merged eligibility-bounded CandidateRanker seam
• include shared heterogeneous-routing and IICP-E050 credential-lifecycle evidence
• update package/runtime version truth and immutable release notes

Compatibility

• additive, opt-in local selection hook
• no wire change
• built-in selection remains the fallback
• IICP retains policy, revalidation, and dispatch authority

Local evidence

• Ruff passed
• mypy no-regression baseline passed (74/74 existing findings)
• pytest: 1150 passed, 2 skipped
• sdist and wheel built successfully

Release lane

This PR prepares source only. Publication remains a separate guarded local action after merge.