✨(summary) link transcript to their downloadable recording

Link the transcription document to its related recording by adding a short
header explaining that users can download the audio file via a dedicated link.

This was a highly requested feature, as many users need to keep their audio
files.

As part of a small refactor, remove the argument length check in the metadata
analytics class. The hardcoded argument count made code evolution harder and was
easy to forget updating. Argument unwrapping remains fragile and should be
redesigned later to be more robust.

The backend is responsible for generating the download link to ensure
consistency and reliability.

I tried adding a divider, but the Markdown-to-Yjs conversion is very lossy and
almost never handles it correctly. Only about one out of ten conversions works
as expected.

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

@@ -16,6 +16,23 @@ from core import models
 logger = logging.getLogger(__name__)
 
 
+def get_recording_download_base_url() -> str:
+    """Get the recording download base URL with backward compatibility."""
+    new_setting = settings.RECORDING_DOWNLOAD_BASE_URL
+    old_setting = settings.SCREEN_RECORDING_BASE_URL
+
+    if old_setting:
+        logger.warning(
+            "SCREEN_RECORDING_BASE_URL is deprecated and will be removed in a future version. "
+            "Please use RECORDING_DOWNLOAD_BASE_URL instead."
+        )
+
+    if new_setting:
+        return new_setting
+
+    return old_setting
+
+
 class NotificationService:
     """Service for processing recordings and notifying external services."""
 
@@ -69,7 +86,7 @@ class NotificationService:
             "domain": settings.EMAIL_DOMAIN,
             "room_name": recording.room.name,
             "recording_expiration_days": settings.RECORDING_EXPIRATION_DAYS,
-            "link": f"{settings.SCREEN_RECORDING_BASE_URL}/{recording.id}",
+            "link": f"{get_recording_download_base_url()}/{recording.id}",
         }
 
         has_failures = False
@@ -149,6 +166,7 @@ class NotificationService:
             "recording_time": recording.created_at.astimezone(
                 owner_access.user.timezone
             ).strftime("%H:%M"),
+            "download_link": f"{get_recording_download_base_url()}/{recording.id}",
         }
 
         headers = {