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.test.ts

@@ -1,17 +1,18 @@
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 
 import { AIStore } from "./index.js";
+import type { SessionRow } from "./index.js";
 import type { AISessionPersistence } from "./index.js";
 
 /** A simple in-memory persistence backend for tests. */
 function memoryPersistence(): AISessionPersistence {
-  const rows = new Map<string, unknown>();
+  const rows = new Map<string, SessionRow>();
   return {
     list: async (projectId) =>
       Array.from(rows.values())
         .filter((r) => r.projectId === projectId)
         .map((r) => ({ ...r })),
-    get: async (id) => (rows.has(id) ? { ...rows.get(id) } : null),
+    get: async (id) => (rows.has(id) ? ({ ...rows.get(id) } as SessionRow) : null),
     save: async (session) => {
       rows.set(session.id, { ...session });
     },
@@ -62,10 +63,8 @@ describe("AIStore", () => {
   it("adds a message to a session", async () => {
     const session = await store.createSession();
     const updated = await store.addMessage(session.id, {
-      id: "m1",
       role: "user",
       content: "hello",
-      createdAt: "2026-01-01T00:00:00.000Z",
     });
     expect(updated.messages).toHaveLength(1);
     expect(updated.messages[0]?.role).toBe("user");
@@ -74,14 +73,12 @@ describe("AIStore", () => {
   it("adds a suggestion and lists it", async () => {
     const session = await store.createSession();
     const updated = await store.addSuggestion(session.id, {
-      id: "s1",
       sessionId: session.id,
       kind: "brainstorm",
       title: "Ideas",
       text: "some ideas",
       summary: "summary",
       status: "pending",
-      createdAt: "2026-01-01T00:00:00.000Z",
     });
     expect(updated.suggestions).toHaveLength(1);
     const list = await store.listSuggestions(session.id);