refactor(logging): preserve tracebacks and add channel context

- Preserve tracebacks: logger.error in except blocks → logger.exception
- Channel context: BaseChannel injects self.logger = logger.bind(channel=name)
- Third-party bridge: redirect_lib_logging() replaces ad-hoc stdlib-to-loguru bridges
- Log levels: network timeouts downgraded from ERROR → WARNING
- Fix --verbose flag to actually work with loguru (set handler to DEBUG)

nanobot/heartbeat/service.py

@@ -144,8 +144,8 @@ class HeartbeatService:
                     await self._tick()
             except asyncio.CancelledError:
                 break
-            except Exception as e:
-                logger.error("Heartbeat error: {}", e)
+            except Exception:
+                logger.exception("Heartbeat error")
 
     @staticmethod
     def _is_deliverable(response: str) -> bool: