refactor(app): introduce attachment storage layer and draft lifecycle management

Replace inline data-URL image handling with a persistent attachment storage service, add draft lifecycle states (active/abandoned/sent) with generation tracking, and update fetchAgent to return project placement alongside agent snapshots.

packages/app/src/stores/draft-keys.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { buildDraftStoreKey } from "./draft-keys";
+
+describe("buildDraftStoreKey", () => {
+  it("isolates agent drafts by server and agent ids", () => {
+    const keyA = buildDraftStoreKey({
+      serverId: "server-a",
+      agentId: "agent-1",
+    });
+    const keyB = buildDraftStoreKey({
+      serverId: "server-b",
+      agentId: "agent-1",
+    });
+    const keyC = buildDraftStoreKey({
+      serverId: "server-a",
+      agentId: "agent-2",
+    });
+
+    expect(keyA).not.toBe(keyB);
+    expect(keyA).not.toBe(keyC);
+    expect(keyB).not.toBe(keyC);
+  });
+
+  it("uses draftId keyspace for create flow drafts", () => {
+    const key = buildDraftStoreKey({
+      serverId: "server-a",
+      agentId: "__new_agent__",
+      draftId: "draft-123",
+    });
+
+    expect(key).toBe("draft:server-a:draft-123");
+  });
+});