chore: consume releases with packaged API contracts

[earguinarena]

Summary

• Updates examples to the published runtime and CDK releases containing agent-readable API contracts.
• Keeps all dependencies sourced from PyPI.
• Verifies contract resolution from installed distributions.

Published artifacts

• lambda-api-decorators==0.3.4
• lambda-api-decorators-cdk==0.4.7

Validation

• PyPI wheel and sdist inspection: passed; both artifacts per package contain _agent/api-contract.json and _agent/behavior.md, schema 1.0, valid JSON, no package version in contract, exact distribution metadata.
• Installed-distribution contract resolution: passed (source_kind: installed, metadata versions 0.3.4/0.4.7).
• Direct wheel contract resolution: passed (source_kind: wheel, metadata versions 0.3.4/0.4.7).
• Example test suites: 36 passed, 15 skipped because Docker daemon access is unavailable locally.
• Full suite: passed with the same 15 explicit Docker skips.
• compileall: passed.
• CDK synth: attempted for all four examples; blocked by Docker socket permission denied during bundling. CI must run synth without skips.
• Agent audit: passed with no warnings.
• git diff --check: passed.

Documentation gate

The documentation PR must remain unmerged until this PR is integrated.