Implement the 007-add-knip feature that adds Knip unused code detection to the quality gate and as a standalone command

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/007-add-knip/quickstart.md

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+# Quickstart: Add Knip Unused Code Detection
+
+**Date**: 2026-03-05
+
+## What This Feature Does
+
+Adds Knip to the project to detect unused files, exports, dependencies, devDependencies, and types across the pnpm workspace. Enforces it as part of the `pnpm check` quality gate (which runs on every commit via Lefthook).
+
+## Files Changed
+
+| File | Change |
+|------|--------|
+| `package.json` | Add `knip` devDependency; add `knip` script; update `check` script |
+| `knip.json` (new) | Workspace-aware Knip configuration |
+
+## How to Use
+
+```bash
+# Run unused-code check standalone
+pnpm knip
+
+# Run full quality gate (now includes Knip)
+pnpm check
+```
+
+## Verification
+
+1. `pnpm check` passes on the current codebase (no false positives).
+2. Add an unused export to any file → `pnpm knip` reports it → `pnpm check` fails.