chore: streamline shared agent guidance

[Chemaclass]

Background

Contributor guidance repeated checks and described obsolete runner and release behavior. Shorter shared specs make the required steps clearer for Claude Code and Codex.

Changes

• Reduce root, rule and skill entrypoint wording by 26% while preserving model tiers and agent roles.
• Align runtime references, release preparation, coverage measurement and PR formatting with the current repository.
• Remove duplicate validation and unsafe issue-queue commands; regenerate and validate both targets.
• Verify sequential and parallel suites, static analysis and formatting.

Checklist

• I updated the CHANGELOG.md to reflect the new feature or fix
• I updated the documentation to reflect the changes