refactor: async I/O, input sanitisation, and shared utilities cleanup

plugins/common.py

@@ -55,3 +55,28 @@ def is_public_destination(target: str) -> bool:
     except Exception as e:
         logger.warning(f"Cannot resolve {target}: {e}")
         return False
+
+async def handle_command(room, message, bot, prefix, config):
+    """No-op handler so the bot doesn't crash when loading this module as a plugin."""
+    pass
+
+async def send_html_message(bot, room_id, html_body, markdown_fallback):
+    """Send an HTML-formatted message with a Markdown fallback.
+
+    Args:
+        bot: simplematrixbotlib.Bot instance
+        room_id: Matrix room ID
+        html_body: HTML string (table, etc.)
+        markdown_fallback: Markdown/plain text for clients that don't render HTML
+    """
+    content = {
+        "msgtype": "m.text",
+        "body": markdown_fallback,
+        "format": "org.matrix.custom.html",
+        "formatted_body": html_body
+    }
+    await bot.async_client.room_send(
+        room_id=room_id,
+        message_type="m.room.message",
+        content=content
+    )