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/channels/test_telegram_channel.py

@@ -306,17 +306,19 @@ async def test_on_error_logs_network_issues_as_warning(monkeypatch) -> None:
     recorded: list[tuple[str, str]] = []
 
     monkeypatch.setattr(
-        "nanobot.channels.telegram.logger.warning",
+        channel.logger,
+        "warning",
         lambda message, error: recorded.append(("warning", message.format(error))),
     )
     monkeypatch.setattr(
-        "nanobot.channels.telegram.logger.error",
+        channel.logger,
+        "error",
         lambda message, error: recorded.append(("error", message.format(error))),
     )
 
     await channel._on_error(object(), SimpleNamespace(error=NetworkError("proxy disconnected")))
 
-    assert recorded == [("warning", "Telegram network issue: proxy disconnected")]
+    assert recorded == [("warning", "network issue: proxy disconnected")]
 
 
 @pytest.mark.asyncio
@@ -330,13 +332,14 @@ async def test_on_error_summarizes_empty_network_error(monkeypatch) -> None:
     recorded: list[tuple[str, str]] = []
 
     monkeypatch.setattr(
-        "nanobot.channels.telegram.logger.warning",
+        channel.logger,
+        "warning",
         lambda message, error: recorded.append(("warning", message.format(error))),
     )
 
     await channel._on_error(object(), SimpleNamespace(error=NetworkError("")))
 
-    assert recorded == [("warning", "Telegram network issue: NetworkError")]
+    assert recorded == [("warning", "network issue: NetworkError")]
 
 
 @pytest.mark.asyncio
@@ -348,17 +351,19 @@ async def test_on_error_keeps_non_network_exceptions_as_error(monkeypatch) -> No
     recorded: list[tuple[str, str]] = []
 
     monkeypatch.setattr(
-        "nanobot.channels.telegram.logger.warning",
+        channel.logger,
+        "warning",
         lambda message, error: recorded.append(("warning", message.format(error))),
     )
     monkeypatch.setattr(
-        "nanobot.channels.telegram.logger.error",
+        channel.logger,
+        "error",
         lambda message, error: recorded.append(("error", message.format(error))),
     )
 
     await channel._on_error(object(), SimpleNamespace(error=RuntimeError("boom")))
 
-    assert recorded == [("error", "Telegram error: boom")]
+    assert recorded == [("error", "error: boom")]
 
 
 @pytest.mark.asyncio