chore: add local lefthook guard auto-installed via prepare

Replace the empty lefthook.yml with real pre-commit (typecheck) and
pre-push (typecheck, test) hooks mirroring ci.yml, and add a prepare
script so npm install auto-installs them. Local guard before push, ci.yml
still gates merges.

Author: ph33nx

lefthook.yml

@@ -0,0 +1,16 @@
+# Local CI guard. Mirrors .github/workflows/ci.yml so broken code never reaches a push.
+# Auto-installed via the package.json prepare script on npm install.
+pre-commit:
+  parallel: true
+  commands:
+    typecheck:
+      run: npx tsc --noEmit
+pre-push:
+  parallel: false
+  commands:
+    typecheck:
+      run: npx tsc --noEmit
+      priority: 1
+    test:
+      run: npm test
+      priority: 2

package-lock.json

@@ -8,7 +8,8 @@
     "ios": "expo start --ios",
     "web": "expo start --web",
     "typecheck": "tsc --noEmit",
-    "test": "jest"
+    "test": "jest",
+    "prepare": "lefthook install"
   },
   "jest": {
     "preset": "jest-expo/node"
@@ -42,6 +43,7 @@
     "babel-preset-expo": "~56.0.0",
     "jest": "~29.7.0",
     "jest-expo": "~56.0.5",
+    "lefthook": "^2.1.9",
     "typescript": "~6.0.3"
   },
   "private": true