Add feed health observability and repaired source overlays

[MEHuggins]

Purpose

Replace silent feed failures with explicit health reporting, repair the previously empty critical lanes, and keep the merge review free of generated-feed churn.

Included changes

• Adds an independent post-build feed-health auditor and critical-lane gate.
• Adds machine-readable, Markdown, and HTML health reports during live feed runs.
• Distinguishes healthy, degraded, stale last-known-good, empty, and critical states.
• Adds source-level HTTP, redirect, blocking, and link-discovery diagnostics.
• Adds reviewed source overlays for agentic AI, Elon Musk, quantum security, bio-computation, AI insurance/liability, intuition neuroscience, and preprint servers.
• Adds a dedicated artificial-womb/artificial-placenta overlay covering Vitara EXTEND publications, CHOP, UWA EVE, Eindhoven Perinatal Life Support, Michigan Medicine, and FDA regulatory material.
• Makes gzip deterministic and prevents Python cache files from entering commits.
• Adds unit tests and separates ordinary PR validation from health output generated only during a live rebuild.

Live validation already completed

The implementation was tested on the isolated integration branch. The successful live run rebuilt all 111 areas and passed the final critical-feed gate with:

• 0 critical areas
• 0 empty areas
• repaired critical lanes populated with current items

Clean-review guarantee

This branch is based on current main and contains exactly nine intentional files. It excludes generated feeds, generated health snapshots, root-index churn, and __pycache__ files.

Safety

• Draft PR only.
• No merge has been performed.
• main remains unchanged.