500 response on deleting a project's default dashboard

[mshriver]

When a user attempts to delete a dashboard that is a project default, a 500 occurs on the backend.

192.168.86.60 - - [12/Feb/2025 12:24:46] "DELETE /api/dashboard/2656b519-07d2-4f5f-8fc8-0904b97a1d5b HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/mnt/.backend_env/lib/python3.9/site-packages/sqlalchemy/engine/base.py", line 1276, in _execute_context
    self.dialect.do_execute(
  File "/mnt/.backend_env/lib/python3.9/site-packages/sqlalchemy/engine/default.py", line 608, in do_execute
    cursor.execute(statement, parameters)
psycopg2.errors.ForeignKeyViolation: update or delete on table "dashboards" violates foreign key constraint "projects_default_dashboard_id_fkey" on table "projects"
DETAIL:  Key (id)=(2656b519-07d2-4f5f-8fc8-0904b97a1d5b) is still referenced from table "projects".

The delete function in the backend needs to account for project's default dashboard selection, and clear that first before deleting the record.

After removing the default dashboard configuration for the project, the dashboard can be deleted successfully.