Add "Sessions" as a Data Source in Dashboard Widgets

[AkioNuernberger]

Describe the feature or potential improvement

Currently, when creating a custom widget in the Langfuse Dashboard, the "Data Selection" -> "View" dropdown only allows users to select Traces, Observations, or Scores.

There is no native way to select Sessions as the primary data source. This makes it difficult to visualize high-level session metrics, such as the number of unique user sessions over time, without relying on complex downstream calculations or external BI tools.

Describe the solution you'd like I would like to see "Sessions" added as an option in the "View" dropdown within the "Widget Configuration" pane (see attached screenshot).

Location: Dashboard -> Edit/New Widget -> Data Selection -> View.

Behavior: When "Sessions" is selected, the "Metric" dropdown should update to support session-level metrics (e.g., Count of unique sessions, Average Session Duration, Total Cost per Session).

Describe alternatives you've considered:

• Counting unique session_ids via the "Traces" view (currently not supported as a direct "Count Unique" metric in the widget UI).
• Exporting data via API and building dashboards in external tools (e.g., PostHog or Mixpanel), which adds unnecessary friction.

Additional information

No response