Polish content-health-monitor

We can fold in the functionality of prototype-content-with-issues-table in connect-staging-extensions (surfaces content whose latest deployment/job has failed), before then deleting prototype-content-with-issues-table. content-health-monitor becomes a single scheduled content-health report covering both content/URL uptime and failed deployments/jobs. We could optionally also roll a third prong into the new-and-improved content-health-monitor: surfacing orphaned content (content owned by deactivated/departed users or that's been unused/unviewed for a long time).

Baselines:

• Rewrite README for the multi-prong report: what it does, who it's for, setup/config, how to use
• Rewrite description: concise, states functionality + value
• Make the report self-demonstrating: surface its own mechanism (e.g. "checked N items as {you} on {date}")
• Add why-comments to the source

App-specific:

• Port the prototype's failed-job logic from R to Python/posit-sdk
• Add the failed-deployments/jobs prong
• (Optional) add an orphaned-content prong (deactivated owners / long-unused)
• Handle scale: memoize owner-email lookups, avoid full-list scans, paginate
• Extend tests to cover the new prongs; add CI
• Refactor test_integration.py to exercise the real .qmd
• Remove dead deps; delete prototype-content-with-issues-table
• Bump version, CHANGELOG, checksums

Start by reading the existing content-health-monitor and prototype-content-with-issues-table, including their README files and the .qmd used by test_integration.py. Compare the prototype's R failed-job logic with the Python/posit-sdk implementation, then map the requested report prongs, tests, CI, dependencies, version, CHANGELOG, and checksums. Done requires the combined report, updated documentation and tests, and removal of the prototype.