feat(KB-330): rename internal packages from @kb/* to @fusion/*

- Rename @kb/core, @kb/dashboard, @kb/engine to @fusion/* namespace
- Update all import statements across 143+ files to use new package names
- Update workspace dependencies and root package.json references
- Fix bundler configurations (tsup, vite) for new package names
- Update test files and fix typecheck issues
- Add changeset file documenting the package rename

packages/dashboard/src/__tests__/websocket.test.ts

@@ -1,7 +1,7 @@
 import { EventEmitter, once } from "node:events";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { WebSocket } from "ws";
-import type { Task } from "@kb/core";
+import type { Task } from "@fusion/core";
 import { createServer } from "../server.js";
 import { WebSocketManager } from "../websocket.js";
 import { InMemoryBadgePubSub, type BadgePubSub } from "../badge-pubsub.js";