feat(tags): Implement tagged task lists migration system (Part 1/2)

This commit introduces the foundational infrastructure for tagged task lists,
enabling multi-context task management without remote storage to prevent merge conflicts.

CORE ARCHITECTURE:
• Silent migration system transforms tasks.json from old format { "tasks": [...] }
  to new tagged format { "master": { "tasks": [...] } }
• Tag resolution layer provides complete backward compatibility - existing code continues to work
• Automatic configuration and state management for seamless user experience

SILENT MIGRATION SYSTEM:
• Automatic detection and migration of legacy tasks.json format
• Complete project migration: tasks.json + config.json + state.json
• Transparent tag resolution returns old format to maintain compatibility
• Zero breaking changes - all existing functionality preserved

CONFIGURATION MANAGEMENT:
• Added global.defaultTag setting (defaults to 'master')
• New tags section with gitIntegration placeholders for future features
• Automatic config.json migration during first run
• Proper state.json creation with migration tracking

USER EXPERIENCE:
• Clean, one-time FYI notice after migration (no emojis, professional styling)
• Notice appears after 'Suggested Next Steps' and is tracked in state.json
• Silent operation - users unaware migration occurred unless explicitly shown

TECHNICAL IMPLEMENTATION:
• Enhanced readJSON() with automatic migration detection and processing
• New utility functions: getCurrentTag(), resolveTag(), getTasksForTag(), setTasksForTag()
• Complete migration orchestration via performCompleteTagMigration()
• Robust error handling and fallback mechanisms

BACKWARD COMPATIBILITY:
• 100% backward compatibility maintained
• Existing CLI commands and MCP tools continue to work unchanged
• Legacy tasks.json format automatically upgraded on first read
• All existing workflows preserved

TESTING VERIFIED:
• Complete migration from legacy state works correctly
• Config.json properly updated with tagged system settings
• State.json created with correct initial values
• Migration notice system functions as designed
• All existing functionality continues to work normally

Part 2 will implement tag management commands (add-tag, use-tag, list-tags)
and MCP tool updates for full tagged task system functionality.

Related: Task 103 - Implement Tagged Task Lists System for Multi-Context Task Management

.taskmaster/config.json

@@ -1,33 +1,41 @@
 {
-	"models": {
-		"main": {
-			"provider": "anthropic",
-			"modelId": "claude-sonnet-4-20250514",
-			"maxTokens": 50000,
-			"temperature": 0.2
-		},
-		"research": {
-			"provider": "perplexity",
-			"modelId": "sonar-pro",
-			"maxTokens": 8700,
-			"temperature": 0.1
-		},
-		"fallback": {
-			"provider": "anthropic",
-			"modelId": "claude-3-7-sonnet-20250219",
-			"maxTokens": 128000,
-			"temperature": 0.2
-		}
-	},
-	"global": {
-		"userId": "1234567890",
-		"logLevel": "info",
-		"debug": false,
-		"defaultSubtasks": 5,
-		"defaultPriority": "medium",
-		"projectName": "Taskmaster",
-		"ollamaBaseURL": "http://localhost:11434/api",
-		"bedrockBaseURL": "https://bedrock.us-east-1.amazonaws.com",
-		"azureBaseURL": "https://your-endpoint.azure.com/"
-	}
-}
+  "models": {
+    "main": {
+      "provider": "anthropic",
+      "modelId": "claude-sonnet-4-20250514",
+      "maxTokens": 50000,
+      "temperature": 0.2
+    },
+    "research": {
+      "provider": "perplexity",
+      "modelId": "sonar-pro",
+      "maxTokens": 8700,
+      "temperature": 0.1
+    },
+    "fallback": {
+      "provider": "anthropic",
+      "modelId": "claude-3-7-sonnet-20250219",
+      "maxTokens": 128000,
+      "temperature": 0.2
+    }
+  },
+  "global": {
+    "userId": "1234567890",
+    "logLevel": "info",
+    "debug": false,
+    "defaultSubtasks": 5,
+    "defaultPriority": "medium",
+    "projectName": "Taskmaster",
+    "ollamaBaseURL": "http://localhost:11434/api",
+    "bedrockBaseURL": "https://bedrock.us-east-1.amazonaws.com",
+    "azureBaseURL": "https://your-endpoint.azure.com/",
+    "defaultTag": "master"
+  },
+  "tags": {
+    "autoSwitchOnBranch": false,
+    "gitIntegration": {
+      "enabled": false,
+      "autoSwitchTagWithBranch": false
+    }
+  }
+}

.taskmaster/state.json

@@ -0,0 +1,6 @@
+{
+  "currentTag": "master",
+  "lastSwitched": "2025-06-11T20:26:12.598Z",
+  "branchTagMapping": {},
+  "migrationNoticeShown": true
+}

.taskmaster/tasks/task_103.txt

@@ -25,13 +25,13 @@
 - Run automated and manual tests for all new and modified commands, including edge cases (e.g., duplicate tag names, tag deletion with tasks).
 
 # Subtasks:
-## 1. Design Extended tasks.json Schema for Tag Support [pending]
+## 1. Design Extended tasks.json Schema for Tag Support [done]
 ### Dependencies: None
 ### Description: Define and document the updated tasks.json schema to include a 'tags' structure, ensuring 'master' is the default tag containing all existing tasks.
 ### Details:
 Create a schema that supports multiple tags, with backward compatibility for users without tags.
 
-## 2. Implement Seamless Migration for Existing Users [pending]
+## 2. Implement Seamless Migration for Existing Users [done]
 ### Dependencies: 103.1
 ### Description: Develop a migration script or logic to move existing tasks into the 'master' tag for users upgrading from previous versions.
 ### Details:
@@ -112,7 +112,7 @@ Ensure all features work as intended and meet quality standards, with specific f
 ### Details:
 
 
-## 15. Implement Tasks.json Migration Logic [pending]
+## 15. Implement Tasks.json Migration Logic [done]
 ### Dependencies: 103.1, 103.2
 ### Description: Create specific migration logic to transform existing tasks.json format (array of tasks) to the new tagged format ({tags: {master: {tasks: [...]}}}). Include validation and rollback capabilities.
 ### Details: