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)

tests/agent/test_runner.py

@@ -643,7 +643,7 @@ def test_persist_tool_result_logs_cleanup_failures(monkeypatch, tmp_path):
         lambda *_args, **_kwargs: (_ for _ in ()).throw(OSError("busy")),
     )
     monkeypatch.setattr(
-        "nanobot.utils.helpers.logger.warning",
+        "nanobot.utils.helpers.logger.exception",
         lambda message, *args: warnings.append(message.format(*args)),
     )