fix(config): wire tasktool defaults in DefaultConfig and fix env tags

- Add TaskTool entry to DefaultConfig() with enabled:true and the four
  icon defaults (🔘/🟡/🟢/🔴), matching the documented defaults
- Replace dead default:"..." struct tags on TaskToolIconsConfig with the
  correct caarlos0/env v11 format env:"VAR,default=VALUE" so env overrides
  actually work; previously the bare default: tag was silently ignored

pkg/config/config.go

@@ -675,10 +675,10 @@ type TaskToolConfig struct {
 }
 
 type TaskToolIconsConfig struct {
-	Pending    string `json:"pending"     env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_PENDING"    default:"🔘"`
-	InProgress string `json:"in_progress" env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_IN_PROGRESS" default:"🟡"`
-	Completed  string `json:"completed"   env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_COMPLETED"  default:"🟢"`
-	Failed     string `json:"failed"      env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_FAILED"     default:"🔴"`
+	Pending    string `json:"pending"     env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_PENDING,default=🔘"`
+	InProgress string `json:"in_progress" env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_IN_PROGRESS,default=🟡"`
+	Completed  string `json:"completed"   env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_COMPLETED,default=🟢"`
+	Failed     string `json:"failed"      env:"PICOCLAW_TOOLS_TASK_TOOL_ICONS_FAILED,default=🔴"`
 }
 
 type SearchCacheConfig struct {

pkg/config/defaults.go

@@ -452,6 +452,17 @@ func DefaultConfig() *Config {
 			WriteFile: ToolConfig{
 				Enabled: true,
 			},
+			TaskTool: TaskToolConfig{
+				ToolConfig: ToolConfig{
+					Enabled: true,
+				},
+				Icons: TaskToolIconsConfig{
+					Pending:    "🔘",
+					InProgress: "🟡",
+					Completed:  "🟢",
+					Failed:     "🔴",
+				},
+			},
 		},
 		Heartbeat: HeartbeatConfig{
 			Enabled:  true,