fix: use data.key instead of data.data in series_updated handler

The websocket-client strips the outer {type, data, ...} wrapper before
emitting to handlers, so handlers receive the inner series data object
directly (e.g. {key, name, missing_episodes}) — not {type, data: {...}}.

The series_updated handler was checking data.data which always failed,
causing every update to fall back to a full loadSeries() call instead of
calling updateSingleSeries() directly. This prevented the missing
episodes count from updating in real-time after a download completed.

Fix: check data.key directly and pass data (not data.data) to
updateSingleSeries().

uv.lock

@@ -0,0 +1,3 @@
+version = 1
+revision = 3
+requires-python = ">=3.12"