✨(summary) add a language parameter for transcription

Pass recording options’ language to the summary service, allowing users to
personalize the recording language.

This is important because automatic language detection often fails, causing
empty transcriptions or 5xx errors from the Whisper API. Users then do not
receive their transcriptions, which leads to frustration. For most of our
userbase, meetings are in French, and automatic detection is unreliable.

Support for language parameterization in the Whisper API has existed for some
time; only the frontend and backend integration were missing.

I did not force French as the default, since a minority of users hold English or
other European meetings. A proper settings tab to configure this value will be
introduced later.

src/backend/core/recording/event/notification.py

@@ -137,6 +137,7 @@ class NotificationService:
             "email": owner_access.user.email,
             "sub": owner_access.user.sub,
             "room": recording.room.name,
+            "language": recording.options.get("language"),
             "recording_date": recording.created_at.astimezone(
                 owner_access.user.timezone
             ).strftime("%Y-%m-%d"),