docs: lefthook - Align setup and rollback guidance #387

Documentation Update Summary

Make docs/LEFTHOOK_SETUP.md accurately describe current npm-based installation and hook behaviour.

What documentation is needed?

Replace obsolete pnpm instructions with verified npm commands and the locally installed Lefthook executable. Document recovery after npm ci --ignore-scripts, staged-path triggers versus whole-directory validation, bypass limitations and corrected uninstall sequencing/lifecycle references. Remove ineffective positional-filename troubleshooting. Describe vite build as bundling, not semantic type checking.

Acceptance Criteria

• Commands exercised in disposable fixtures.
• Installation and rollback do not fetch an unrelated CLI version.
• Documentation matches recorded behaviour and links lifecycle evidence.

Dependencies

Finalise alongside installation/rollback, staging/operation and existing-gate verification children. No package-manager migration.

Definition of Ready

• Scope, fixtures, prerequisites and overlap identified.

Definition of Done

• Criteria pass; revision, environment, commands and exit codes recorded.
• Documentation reflects tested behaviour; applicable review/checks pass.

Branch instructions

Recheck repository instructions, active work and PR template before implementation. Use an independently reviewable branch from develop; do not reuse merged branches automatically. Preserve unrelated changes; no force-push, merge or deployment.

Estimate intentionally unset. No deadline, milestone or release commitment.