fix: 将所有emoji/Unicode特殊字符替换为ASCII安全字符

Windows cmd/PowerShell默认codepage下emoji显示为?号。
全局替换: 👋->移除, 💭->[Thinking], ⚙->*, ✓->[OK], ✗->[FAIL],
◆->>, ⚠->[!], ✅->[OK], •->|/-, →->>>, ✏️->[Edit]等。
❯保留（windows-vtp终端下正常显示）。

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

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

@@ -24,6 +24,6 @@ public class ClearCommand implements SlashCommand {
         if (context.agentLoop() != null) {
             context.agentLoop().reset();
         }
-        return AnsiStyle.green("  ✓ Conversation history cleared.");
+        return AnsiStyle.green("  [OK] Conversation history cleared.");
     }
 }

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

@@ -27,8 +27,8 @@ public class CompactCommand implements SlashCommand {
         if (context.agentLoop() != null) {
             int before = context.agentLoop().getMessageHistory().size();
             context.agentLoop().reset();
-            return AnsiStyle.green("  ✓ Context compacted: " + before + " messages → 1 (system prompt only)");
+            return AnsiStyle.green("  [OK] Context compacted: " + before + " messages -> 1 (system prompt only)");
         }
-        return AnsiStyle.yellow("  ⚠ No active conversation to compact.");
+        return AnsiStyle.yellow("  [!] No active conversation to compact.");
     }
 }

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

@@ -38,7 +38,7 @@ public class ModelCommand implements SlashCommand {
 
         if (args != null && !args.isBlank()) {
             sb.append("\n");
-            sb.append(AnsiStyle.yellow("  ⚠ Model switching not yet implemented. Set AI_MODEL env variable."));
+            sb.append(AnsiStyle.yellow("  [!] Model switching not yet implemented. Set AI_MODEL env variable."));
         }
 
         return sb.toString();