fix: ensure API key detection properly reads .env in MCP context

Problem:
- Task Master model configuration wasn't properly checking for API keys in the project's .env file when running through MCP
- The isApiKeySet function was only checking session.env and process.env but not inspecting the .env file directly
- This caused incorrect API key status reporting in MCP tools even when keys were properly set in .env

Solution:
- Modified resolveEnvVariable function in utils.js to properly read from .env file at projectRoot
- Updated isApiKeySet to correctly pass projectRoot to resolveEnvVariable
- Enhanced the key detection logic to have consistent behavior between CLI and MCP contexts
- Maintains the correct precedence: session.env → .env file → process.env

Testing:
- Verified working correctly with both MCP and CLI tools
- API keys properly detected in .env file in both contexts
- Deleted .cursor/mcp.json to confirm introspection of .env as fallback works

.taskmasterconfig

@@ -1,31 +1,31 @@
 {
-  "models": {
-    "main": {
-      "provider": "anthropic",
-      "modelId": "claude-3-7-sonnet-20250219",
-      "maxTokens": 100000,
-      "temperature": 0.2
-    },
-    "research": {
-      "provider": "xai",
-      "modelId": "grok-3",
-      "maxTokens": 8700,
-      "temperature": 0.1
-    },
-    "fallback": {
-      "provider": "anthropic",
-      "modelId": "claude-3-5-sonnet-20241022",
-      "maxTokens": 120000,
-      "temperature": 0.2
-    }
-  },
-  "global": {
-    "logLevel": "info",
-    "debug": false,
-    "defaultSubtasks": 5,
-    "defaultPriority": "medium",
-    "projectName": "Taskmaster",
-    "ollamaBaseUrl": "http://localhost:11434/api",
-    "azureOpenaiBaseUrl": "https://your-endpoint.openai.azure.com/"
-  }
-}
+	"models": {
+		"main": {
+			"provider": "anthropic",
+			"modelId": "claude-3-7-sonnet-20250219",
+			"maxTokens": 100000,
+			"temperature": 0.2
+		},
+		"research": {
+			"provider": "perplexity",
+			"modelId": "sonar-pro",
+			"maxTokens": 8700,
+			"temperature": 0.1
+		},
+		"fallback": {
+			"provider": "anthropic",
+			"modelId": "claude-3-5-sonnet-20241022",
+			"maxTokens": 120000,
+			"temperature": 0.2
+		}
+	},
+	"global": {
+		"logLevel": "info",
+		"debug": false,
+		"defaultSubtasks": 5,
+		"defaultPriority": "medium",
+		"projectName": "Taskmaster",
+		"ollamaBaseUrl": "http://localhost:11434/api",
+		"azureOpenaiBaseUrl": "https://your-endpoint.openai.azure.com/"
+	}
+}