docs(dev): add Taskfile and developer documentation

- Add Taskfile.yml with common development tasks
- Add go-task to devbox dependencies
- Create comprehensive README-developer.md covering:
  - Devbox setup and usage
  - Hugo and Docsy basics
  - Task commands reference
  - Development workflow
  - Content creation guide
  - Testing procedures
  - Troubleshooting tips

devbox.json

@@ -5,7 +5,8 @@
     "dart-sass@latest",
     "go@latest",
     "nodejs@latest",
-    "htmltest@latest"
+    "htmltest@latest",
+    "go-task@latest"
   ],
   "shell": {
     "init_hook": [],