ci: widen published smoke propagation retry

[cafitac]

Summary

• Extends the post-publish smoke retry window from 2 minutes to 6 minutes to tolerate PyPI propagation delays that affect npm wrapper npx/npm exec because the npm package delegates to the PyPI core.
• Raises the manual workflow default from 6 to 18 attempts.
• Adds test coverage for the longer retry configuration.

Verification

• uvx --from pyyaml python ... parsed both workflow YAML files
• uv run pytest tests/test_published_install_smoke.py -q -> 11 passed
• uv run pytest tests/ -q -> 145 passed
• uv run python scripts/check_release_metadata.py -> OK
• uv run python scripts/smoke_release_readiness.py -> OK
• git diff --check -> OK

Context

• v0.1.21 npm/PyPI publish succeeded, but the post-publish smoke failed while PyPI still did not expose cafitac-agent-memory==0.1.21 to fresh installs. The script already retries; this PR widens that retry budget.