batch3 T1: session_panes schema + Pane/UserStreamFrame types + sidebar project_id

Adds the session_panes table, Pane/PaneState/PaneCreate/PaneUpdate types,
UserStreamFrame discriminated union, and extends SidebarSession with
project_id (also added to the sidebar SELECT).

apps/server/src/routes/sidebar.ts

@@ -18,7 +18,7 @@ export function registerSidebarRoutes(app: FastifyInstance, sql: Sql): void {
       projects.map(async (p) => {
         const [recent_sessions, countRows] = await Promise.all([
           sql<SidebarSession[]>`
-            SELECT id, name, model, updated_at
+            SELECT id, project_id, name, model, updated_at
             FROM sessions
             WHERE project_id = ${p.id}
             ORDER BY updated_at DESC