refactor: apply BaseSlashCommand to all 54 command implementations

- implements SlashCommand -> extends BaseSlashCommand (all 54 files)
- Replace CommandUtils.parseArgs/args null checks -> args(args)
- Replace agentLoop null checks -> requireAgentLoop(context)/noSession()
- Replace context.agentLoop().getToolContext() -> toolCtx(context)
- Replace CommandUtils.success/error/header/subtitle/warning/info -> instance methods
- Remove unused CommandUtils/AnsiStyle imports where applicable
- 87 tests passing, zero compilation errors

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/java/com/claudecode/command/impl/PlanCommand.java

@@ -1,7 +1,7 @@
 package com.claudecode.command.impl;
 
 import com.claudecode.command.CommandContext;
-import com.claudecode.command.SlashCommand;
+import com.claudecode.command.BaseSlashCommand;
 import com.claudecode.permission.PermissionSettings;
 import com.claudecode.permission.PermissionTypes.PermissionMode;
 
@@ -10,7 +10,7 @@ import com.claudecode.permission.PermissionTypes.PermissionMode;
  * <p>
  * 切换计划模式开关。在计划模式下，AI只能分析不能修改。
  */
-public class PlanCommand implements SlashCommand {
+public class PlanCommand extends BaseSlashCommand {
 
     private final PermissionSettings permissionSettings;