feat: generate README agent index from source files

[cyberpinkman]

What does this PR do?

Adds an auto-generated Agent Index section to README.md, sourced from the repository’s agent markdown files.

This reduces drift between the source agent definitions and the top-level documentation, and adds CI verification so future changes keep the index in sync.

This keeps the existing roster tables untouched and adds a separate generated index for a low-risk discoverability improvement.

Changes

• add scripts/generate-readme-agent-index.sh
• add generated Agent Index section to README.md
• add workflow to verify the generated index on pull requests
• update CONTRIBUTING.md with the regeneration step

Why

The repository now contains a large and growing number of agents across many divisions. Keeping a discoverable index in sync by hand is error-prone. This PR makes that maintenance automatic and reviewable.

Agent Information (if adding/modifying an agent)

• Agent Name: N/A
• Category: docs / tooling
• Specialty: README generation and CI verification

Checklist

• Follows the repository’s shell-script style
• Keeps the generated section scoped to README markers
• Includes CI verification
• Proofread and formatted correctly

[mhc222]

Code Review

No issues found.

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Reviewed by Code Reviewer agent. Issues are only reported at confidence ≥80/100.