refactor: change .exit to /exit for consistency

- Update command from .exit to /exit
- Support both .exit and /exit for backward compatibility
- Update tab completion

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lzwjava

iclaw/completer.py

@@ -17,7 +17,7 @@
     "/clear",
     "/compact",
     "/export",
-    ".exit",
+    "/exit",
 ]
 
 

iclaw/main.py

@@ -44,7 +44,7 @@
     ("/export", "Export full conversation history to JSON file"),
     ("/status", "Show current settings"),
     ("/help", "Show available commands"),
-    (".exit", "Quit"),
+    ("/exit", "Quit"),
 ]
 
 
@@ -99,7 +99,7 @@ def main():
                 print(f"  {cmd:<20} {desc}")
             print()
             continue
-        if user_input == ".exit":
+        if user_input in ("/exit", ".exit"):
             print("Goodbye!")
             break
         if user_input == "/copy":