fix(ai,tasks): Enhance AI provider robustness and task processing

This commit introduces several improvements to AI interactions and
task management functionalities:

- AI Provider Enhancements (for Telemetry & Robustness):
    - :
        - Added a check in  to ensure
          is a string, throwing an error if not. This prevents downstream
           errors (e.g., in ).
    - , , :
        - Standardized return structures for their respective
          and  functions to consistently include /
          and  fields. This aligns them with other providers (like
          Anthropic, Google, Perplexity) for consistent telemetry data
          collection, as part of implementing subtask 77.14 and similar work.

- Task Expansion ():
    - Updated  to be more explicit
      about using an empty array  for empty  to
      better guide AI output.
    - Implemented a pre-emptive cleanup step in
      to replace malformed  with
      before JSON parsing. This improves resilience to AI output quirks,
      particularly observed with Perplexity.

- Adjusts issue in commands.js where successfulRemovals would be undefined. It's properly invoked from the result variable now.

- Updates supported models for Gemini
These changes address issues observed during E2E tests, enhance the
reliability of AI-driven task analysis and expansion, and promote
consistent telemetry data across multiple AI providers.

.taskmasterconfig

@@ -1,32 +1,32 @@
 {
-  "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-3-7-sonnet-20250219",
-      "maxTokens": 120000,
-      "temperature": 0.2
-    }
-  },
-  "global": {
-    "logLevel": "info",
-    "debug": false,
-    "defaultSubtasks": 5,
-    "defaultPriority": "medium",
-    "projectName": "Taskmaster",
-    "ollamaBaseUrl": "http://localhost:11434/api",
-    "userId": "1234567890",
-    "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-3-7-sonnet-20250219",
+			"maxTokens": 64000,
+			"temperature": 0.2
+		}
+	},
+	"global": {
+		"logLevel": "info",
+		"debug": false,
+		"defaultSubtasks": 5,
+		"defaultPriority": "medium",
+		"projectName": "Taskmaster",
+		"ollamaBaseUrl": "http://localhost:11434/api",
+		"userId": "1234567890",
+		"azureOpenaiBaseUrl": "https://your-endpoint.openai.azure.com/"
+	}
+}