BetterAuth session responses contain only identity fields — workspace
context (workspaceId, currentWorkspaceId) was never returned, causing
"Workspace ID is required" on every guarded endpoint after login.
Add GET /api/workspaces endpoint (AuthGuard only, no WorkspaceGuard)
that returns user workspace memberships with auto-provisioning for
new users. Frontend auth-context now fetches workspaces after session
check and persists the default to localStorage. Race condition in
auto-provisioning is guarded by re-querying inside the transaction.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
