feat(dx): pre-commit hooks for local CI (no remote needed)

Local quality gate that runs on every git commit:
- node --check syntax on staged .js files
- block on new emoji in staged .js/.html/.css (md files allowed)
- block on new console.log/debug/debugger statements
- backend route auth lint (existing npm run lint:routes)
- backend tests (baseline 3 fails, block if grew)

Install: npm run hooks:install (top-level)
Bypass: git commit --no-verify

Skips slow checks when irrelevant files changed (tests/lint only run
if backend touched).

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

package.json

@@ -0,0 +1,9 @@
+{
+  "name": "learnspace",
+  "version": "1.0.0",
+  "private": true,
+  "description": "LearnSpace monorepo root — convenience scripts only",
+  "scripts": {
+    "hooks:install": "sh scripts/install-hooks.sh"
+  }
+}