fix(hooks): make startup non-interactive and repo-scoped

[Disdjj]

Summary

• replace hook-time npx --no-install with npx -y so a missing scoped CLI can be fetched without an interactive prompt
• stop project-root discovery at the nearest Git root to prevent sibling repositories named llmdoc from being misidentified
• add regression coverage and synchronize README, parity checks, and tracked llmdoc knowledge

Validation

• npm test — 36 tests passed
• npm run lint
• npm run typecheck
• npm run check:prompts
• node scripts/check-codex-surface.mjs
• npm run validate:dogfood
• npx @tokenroll/llmdoc status — 0 impacted, 0 dirty