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/utils/helpers.py

@@ -268,8 +268,8 @@ def maybe_persist_tool_result(
     bucket = ensure_dir(root / safe_filename(session_key or "default"))
     try:
         _cleanup_tool_result_buckets(root, bucket)
-    except Exception as exc:
-        logger.warning("Failed to clean stale tool result buckets in {}: {}", root, exc)
+    except Exception:
+        logger.exception("Failed to clean stale tool result buckets in {}", root)
     path = bucket / f"{safe_filename(tool_call_id)}.{suffix}"
     if not path.exists():
         if suffix == "json" and isinstance(content, list):
@@ -540,6 +540,6 @@ def sync_workspace_templates(workspace: Path, silent: bool = False) -> list[str]
         )
         gs.init()
     except Exception:
-        logger.warning("Failed to initialize git store for {}", workspace)
+        logger.exception("Failed to initialize git store for {}", workspace)
 
     return added