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>

utils.py

@@ -0,0 +1,81 @@
+import logging
+from logging.handlers import RotatingFileHandler
+from pathlib import Path
+
+from nio import AsyncClient, RoomSendResponse
+
+from config import MAX_INPUT_LENGTH
+
+
+def setup_logging(level="INFO"):
+    Path("logs").mkdir(exist_ok=True)
+
+    logger = logging.getLogger("matrixbot")
+    logger.setLevel(getattr(logging, level.upper(), logging.INFO))
+
+    file_handler = RotatingFileHandler(
+        "logs/matrixbot.log",
+        maxBytes=10 * 1024 * 1024,
+        backupCount=5,
+    )
+    file_handler.setFormatter(
+        logging.Formatter("%(asctime)s - %(levelname)s - %(message)s")
+    )
+
+    stream_handler = logging.StreamHandler()
+    stream_handler.setFormatter(
+        logging.Formatter("%(asctime)s - %(levelname)s - %(message)s")
+    )
+
+    logger.addHandler(file_handler)
+    logger.addHandler(stream_handler)
+    return logger
+
+
+async def send_text(client: AsyncClient, room_id: str, text: str):
+    logger = logging.getLogger("matrixbot")
+    resp = await client.room_send(
+        room_id,
+        message_type="m.room.message",
+        content={"msgtype": "m.text", "body": text},
+    )
+    if not isinstance(resp, RoomSendResponse):
+        logger.error("send_text failed: %s", resp)
+    return resp
+
+
+async def send_html(client: AsyncClient, room_id: str, plain: str, html: str):
+    logger = logging.getLogger("matrixbot")
+    resp = await client.room_send(
+        room_id,
+        message_type="m.room.message",
+        content={
+            "msgtype": "m.text",
+            "body": plain,
+            "format": "org.matrix.custom.html",
+            "formatted_body": html,
+        },
+    )
+    if not isinstance(resp, RoomSendResponse):
+        logger.error("send_html failed: %s", resp)
+    return resp
+
+
+async def send_reaction(client: AsyncClient, room_id: str, event_id: str, emoji: str):
+    return await client.room_send(
+        room_id,
+        message_type="m.reaction",
+        content={
+            "m.relates_to": {
+                "rel_type": "m.annotation",
+                "event_id": event_id,
+                "key": emoji,
+            }
+        },
+    )
+
+
+def sanitize_input(text: str, max_length: int = MAX_INPUT_LENGTH) -> str:
+    text = text.strip()[:max_length]
+    text = "".join(char for char in text if char.isprintable())
+    return text