fix: strip @botname from commands so /new@TigerNanoBot resolves correctly (#3581)

Commands sent directly to the bot in groups include @botname suffix
(e.g. /compress@TigerNanoBot). get_command() now strips the @anything
part before lookup, matching how Telegram bot menu generates commands.
Fixes all slash commands silently doing nothing when sent with @mention.

Co-authored-by: MacroAnarchy <MacroAnarchy@users.noreply.github.com>

tests/gateway/test_platform_base.py

@@ -62,6 +62,18 @@ class TestMessageEventGetCommand:
         event = MessageEvent(text="/")
         assert event.get_command() == ""
 
+    def test_command_with_at_botname(self):
+        event = MessageEvent(text="/new@TigerNanoBot")
+        assert event.get_command() == "new"
+
+    def test_command_with_at_botname_and_args(self):
+        event = MessageEvent(text="/compress@TigerNanoBot")
+        assert event.get_command() == "compress"
+
+    def test_command_mixed_case_with_at_botname(self):
+        event = MessageEvent(text="/RESET@TigerNanoBot")
+        assert event.get_command() == "reset"
+
 
 class TestMessageEventGetCommandArgs:
     def test_command_with_args(self):