Add Matrix bot Phase 1: core setup + fun commands

Modular bot using matrix-nio[e2e] with E2EE support, deployed as
systemd service on Synapse LXC. Includes 10 commands: help, ping,
8ball, fortune, flip, roll, random, rps, poll, champion.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

callbacks.py

@@ -0,0 +1,60 @@
+import logging
+from functools import wraps
+
+from nio import AsyncClient, RoomMessageText
+
+from config import BOT_PREFIX, MATRIX_USER_ID
+from commands import COMMANDS
+
+logger = logging.getLogger("matrixbot")
+
+
+def handle_command_errors(func):
+    @wraps(func)
+    async def wrapper(client, room_id, sender, args):
+        try:
+            return await func(client, room_id, sender, args)
+        except Exception as e:
+            logger.error(f"Error in command {func.__name__}: {e}", exc_info=True)
+            try:
+                from utils import send_text
+                await send_text(client, room_id, "An unexpected error occurred. Please try again later.")
+            except Exception as e2:
+                logger.error(f"Failed to send error message: {e2}", exc_info=True)
+    return wrapper
+
+
+class Callbacks:
+    def __init__(self, client: AsyncClient):
+        self.client = client
+        # Track the sync token so we ignore old messages on startup
+        self.startup_sync_token = None
+
+    async def message(self, room, event):
+        # Ignore messages from before the bot started
+        if self.startup_sync_token is None:
+            return
+
+        # Ignore our own messages
+        if event.sender == MATRIX_USER_ID:
+            return
+
+        body = event.body.strip() if event.body else ""
+        if not body.startswith(BOT_PREFIX):
+            return
+
+        # Parse command and args
+        without_prefix = body[len(BOT_PREFIX):]
+        parts = without_prefix.split(None, 1)
+        cmd_name = parts[0].lower() if parts else ""
+        args = parts[1] if len(parts) > 1 else ""
+
+        logger.info(f"Command '{cmd_name}' from {event.sender} in {room.room_id}")
+
+        handler_entry = COMMANDS.get(cmd_name)
+        if handler_entry is None:
+            return
+
+        handler, _ = handler_entry
+        wrapped = handle_command_errors(handler)
+        await wrapped(self.client, room.room_id, event.sender, args)