feat: Phase 2 - Sync infrastructure

- Created sync client for communicating with API server
- Implemented conflict resolution strategies (last-write-wins, server-wins, client-wins)
- Added offline change queue for queuing changes when server is unreachable
- Implemented merge logic for local and remote task lists
- Added conflict logging to sync_conflicts.log
- Created bidirectional sync with pull/push operations
- Extended Config struct with sync settings (URL, API key, client ID, strategy, offline queue)
- Added SyncResult display with user-friendly output
- Sync handlers already implemented in Phase 1 (GetChanges, PushChanges)

opal-task/internal/engine/config.go

@@ -16,6 +16,14 @@ type Config struct {
 	ColorOutput    bool   `mapstructure:"color_output"`
 	WeekStartDay   string `mapstructure:"week_start_day"`
 	DefaultDueTime string `mapstructure:"default_due_time"`
+
+	// Sync settings
+	SyncEnabled      bool   `mapstructure:"sync_enabled"`
+	SyncURL          string `mapstructure:"sync_url"`
+	SyncAPIKey       string `mapstructure:"sync_api_key"`
+	SyncClientID     string `mapstructure:"sync_client_id"`
+	SyncStrategy     string `mapstructure:"sync_strategy"`
+	SyncQueueOffline bool   `mapstructure:"sync_queue_offline"`
 }
 
 var globalConfig *Config
@@ -79,6 +87,14 @@ func LoadConfig() (*Config, error) {
 	v.SetDefault("week_start_day", "monday")
 	v.SetDefault("default_due_time", "")
 
+	// Sync defaults
+	v.SetDefault("sync_enabled", false)
+	v.SetDefault("sync_url", "")
+	v.SetDefault("sync_api_key", "")
+	v.SetDefault("sync_client_id", "")
+	v.SetDefault("sync_strategy", "last-write-wins")
+	v.SetDefault("sync_queue_offline", true)
+
 	// Try to read existing config
 	err = v.ReadInConfig()
 	if err != nil {
@@ -119,6 +135,14 @@ func SaveConfig(cfg *Config) error {
 	v.Set("week_start_day", cfg.WeekStartDay)
 	v.Set("default_due_time", cfg.DefaultDueTime)
 
+	// Sync settings
+	v.Set("sync_enabled", cfg.SyncEnabled)
+	v.Set("sync_url", cfg.SyncURL)
+	v.Set("sync_api_key", cfg.SyncAPIKey)
+	v.Set("sync_client_id", cfg.SyncClientID)
+	v.Set("sync_strategy", cfg.SyncStrategy)
+	v.Set("sync_queue_offline", cfg.SyncQueueOffline)
+
 	return v.WriteConfig()
 }