feat(bot): add signature verification logging

- Added info-level logging to provide details about signature verification, including secret length and partial hashes for expected and received signatures.
- Helps in debugging signature mismatches without exposing full sensitive data.

systems/x86_64-linux/mx/nextcloud-claude-bot/bot.py

@@ -72,6 +72,8 @@ def verify_signature(body: bytes, signature: str) -> bool:
     if signature.startswith("sha256="):
         signature = signature[7:]
 
+    log.info(f"Signature verification: secret_len={len(BOT_SECRET)}, expected={expected[:16]}..., received={signature[:16]}...")
+
     return hmac.compare_digest(expected, signature)