feat(ai): Integrate OpenAI provider and enhance model config

- Add OpenAI provider implementation using @ai-sdk/openai.\n- Update `models` command/tool to display API key status for configured providers.\n- Implement model-specific `maxTokens` override logic in `config-manager.js` using `supported-models.json`.\n- Improve AI error message parsing in `ai-services-unified.js` for better clarity.

.taskmasterconfig

@@ -1,9 +1,9 @@
 {
   "models": {
     "main": {
-      "provider": "google",
-      "modelId": "gemini-2.5-pro-exp-03-25",
-      "maxTokens": 120000,
+      "provider": "openai",
+      "modelId": "o3-mini",
+      "maxTokens": 100000,
       "temperature": 0.2
     },
     "research": {
@@ -14,7 +14,7 @@
     },
     "fallback": {
       "provider": "anthropic",
-      "modelId": "claude-3-5-sonnet-20241022",
+      "modelId": "claude-3-7-sonnet-20250219",
       "maxTokens": 120000,
       "temperature": 0.2
     }