feat(dashboards): Register Mobile Session Health prebuilt dashboard

[DominikB2014]

Summary

Register the Mobile Session Health prebuilt dashboard in the backend:

• Add MOBILE_SESSION_HEALTH = 13 to the PrebuiltDashboardId enum
• Add dashboard entry to the PREBUILT_DASHBOARDS list with title "Mobile Session Health"

This is part of the mobile session health module migration to the dashboards platform.

[linear]

BROWSE-251 Register mobile session health module in the backend

[sentry]

Bug: The backend adds a new prebuilt dashboard (ID 13), but the frontend's PREBUILT_DASHBOARDS configuration is missing an entry for this ID, which will cause a runtime error on render.
_{Severity: HIGH}

Suggested Fix

Ensure the frontend PR that adds the configuration for the MOBILE_SESSION_HEALTH dashboard (ID 13) to the PrebuiltDashboardId enum and PREBUILT_DASHBOARDS record in prebuiltConfigs.tsx is merged and deployed alongside or before this backend change. The code explicitly notes that backend and frontend configs must be kept in sync.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: src/sentry/dashboards/endpoints/organization_dashboards.py#L77

Potential issue: The backend code introduces a new prebuilt dashboard,
`MOBILE_SESSION_HEALTH`, with an ID of `13`. However, the frontend configuration in
`prebuiltConfigs.tsx` is not updated to include this new dashboard. If this dashboard is
enabled via feature flag or configuration, the backend will create it in the database.
When the frontend attempts to render it, the lookup `PREBUILT_DASHBOARDS[13]` will
return `undefined`. Subsequent code in `prebuiltDashboardRenderer.tsx` that tries to
destructure this `undefined` value (e.g., `const {title, filters} = prebuiltDashboard`)
will throw a runtime error, causing the UI to crash for users viewing this dashboard.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[DominikB2014]

THere will be a frontend PR as well