Add dev-watch recipe with chokidar-cli for live rebuild on CSS/JS changes

- just dev now spawns a background chokidar watcher alongside the PHP server
- CSS/JS changes auto-rebuild into dist/ (~200ms per rebuild)
- just stop kills both the PHP server and the watcher
- just dev-watch still available standalone for split-terminal workflows
- chokidar-cli added as devDependency

package.json

@@ -9,6 +9,7 @@
   },
   "devDependencies": {
     "@biomejs/biome": "^2.3.15",
+    "chokidar-cli": "^3.0.0",
     "lightningcss": "^1.32.0",
     "rolldown": "^1.1.3"
   }