fix: handle dict config in is_allowed() and _validate_allow_from()

getattr() on a dict never finds custom keys — it only searches
object attributes, not dict keys. When channel config is loaded as
a Pydantic extra field (which is a plain dict), getattr(config,
'allow_from', []) always returns the default [], causing all access
to be denied regardless of the allowFrom configuration.

Fix both is_allowed() and _validate_allow_from() to use isinstance
checks, falling back to dict.get() for dict configs while preserving
getattr() for object-style configs.

nanobot/channels/manager.py

@@ -75,7 +75,12 @@ class ChannelManager:
 
     def _validate_allow_from(self) -> None:
         for name, ch in self.channels.items():
-            if getattr(ch.config, "allow_from", None) == []:
+            cfg = ch.config
+            if isinstance(cfg, dict):
+                allow = cfg.get("allow_from") or cfg.get("allowFrom")
+            else:
+                allow = getattr(cfg, "allow_from", None)
+            if allow == []:
                 raise SystemExit(
                     f'Error: "{name}" has empty allowFrom (denies all). '
                     f'Set ["*"] to allow everyone, or add specific user IDs.'