feat(mcp): Add next_step guidance to initialize-project and add tests

Added detailed next_step guidance to the initialize-project MCP tool response,
providing clear instructions about creating a PRD file and using parse-prd
after initialization. This helps users understand the workflow better after
project initialization.

Also added comprehensive unit tests for the initialize-project MCP tool that:
- Verify tool registration with correct parameters
- Test command construction with proper argument formatting
- Check special character escaping in command arguments
- Validate success response formatting including the new next_step field
- Test error handling and fallback mechanisms
- Verify logging behavior

The tests follow the same pattern as other MCP tool tests in the codebase.

tests/fixture/test-tasks.json

@@ -1,14 +1,14 @@
 {
-	"tasks": [
-		{
-			"id": 1,
-			"dependencies": [],
-			"subtasks": [
-				{
-					"id": 1,
-					"dependencies": []
-				}
-			]
-		}
-	]
-}
+  "tasks": [
+    {
+      "id": 1,
+      "dependencies": [],
+      "subtasks": [
+        {
+          "id": 1,
+          "dependencies": []
+        }
+      ]
+    }
+  ]
+}