chore(config): update default AI model to Claude 3.5 Haiku

- Change default model in `package.json` from `claude-3-5-sonnet-latest` to `claude-3-5-haiku-latest`
- Maintain existing configuration structure and enum list

Author: tsdevau

package.json

@@ -62,7 +62,7 @@
       "properties": {
         "diffCommit.model": {
           "type": "string",
-          "default": "claude-3-5-sonnet-latest",
+          "default": "claude-3-5-haiku-latest",
           "enum": [
             "claude-3-5-sonnet-latest",
             "claude-3-5-haiku-latest",