server: reconcile ai_sessions persistence to Chunk 9 AISession shape

Reshape the ai_sessions table (migration 003) and mapping/routes to the
full AISession contract: title, kind, notes, created_at, last_message_at;
drop legacy role/model/settings. toAISession now maps the new columns and
routes create/patch/messages handlers use the new shape.

packages/ai/src/ai-session.ts

@@ -24,7 +24,7 @@ import type {
 } from "@pubscript/core";
 
 /** A persisted session row. */
-interface SessionRow {
+export interface SessionRow {
   id: string;
   projectId: string;
   title: string;
@@ -76,7 +76,8 @@ export function createIndexedDBPersistence(dbName = "pubscript"): AISessionPersi
       return table.where("projectId").equals(projectId).sortBy("updatedAt").then((rows) => rows.reverse());
     },
     async get(id: string) {
-      return table.get(id) ?? null;
+      const row = await table.get(id);
+      return row ?? null;
     },
     async save(row: SessionRow) {
       await table.put(row);