Repair feed pipeline integrity and validation

[MEHuggins]

Why this repair is needed

The hourly Space & Defense workflow filtered feeds.yaml to two areas and then ran the full builder. That periodically rewrote index.html and feeds/all.* as a space-only snapshot. Other writer workflows also lacked a shared lock and could collide during Git pushes.

What this PR changes

• removes the hourly partial-writer behavior
• retains the old space entry point only as a manual full rebuild
• gives every repository-writing workflow the same concurrency lock
• hardens archive commits with full-history checkout, date-based pruning, rebase, and push retries
• replaces best-effort CI with real registry and generated-output validation
• adds reusable validators for feeds.yaml, XML, JSON, and index.html completeness
• removes the misplaced inactive validator workflow
• expands automatic failure issues to all active pipeline workflows
• corrects README status badges and documents the safeguards

Safety

• all changes are isolated on repair/feed-pipeline-integrity
• no feed source entries are removed or altered
• no generated feed content is deleted by this PR
• the main six-hour full rebuild remains the authoritative scheduled writer

Verification before merge

CI must compile the scripts, validate all 2,327 lines of the registry, parse every committed XML/JSON output, and confirm every configured area appears in the public directory.

[github-actions]

Feed registry validation report

ERROR: feeds.yaml validation failed with 1 problem(s):
 - invalid area slug: 'human_effect'