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/notes.test.ts

@@ -97,7 +97,7 @@ describe("NoteBuilder", () => {
 
     const init = calls[0] as RequestInit;
     const body = JSON.parse(init.body as string) as Record<string, unknown>;
-    const messages = body.messages as Array<{ content: string }>;
+    const messages = body.messages as Array<{ content: string; role?: string }>;
     const system = messages.find((m) => m.role === "system")?.content ?? "";
     expect(system).toContain("The Stolen Relic");
   });