Clean up public repository documentation

[josiahking]

Summary

• rewrites public repository guidance around current capabilities instead of internal roadmap chronology
• keeps AGENTS.md public, neutral and tool-compatible
• updates package and development documentation to reflect current ownership and validation behavior
• strengthens documentation-policy tests against internal workflow wording and stale roadmap identifiers

Validation

• Composer validation passed
• Architecture + Documentation: 233 tests, 10914 assertions
• Root quality passed
• Release package validation passed
• Deterministic package split validation passed for all 7 packages
• Skeleton/create-project validation passed
• Prerelease consumer validation passed
• Public wording scan returned no hits