docs: remove internal notes from public package

[claudialnathan]

Summary

• remove private/internal project references from README and public docs
• exclude AGENTS.md and broad docs publishing from npm package contents
• ignore private docs paths and remove public project brief/workflow docs

Verification

• npm --cache /tmp/priors-npm-cache test
• npm --cache /tmp/priors-npm-cache pack --dry-run --json
• npm registry currently has priors@1.0.0-rc.0 only; repo is already 1.0.0-rc.1, so publish 1.0.0-rc.1 after merge