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/server.ts

@@ -3,7 +3,7 @@ import { randomUUID } from "node:crypto";
 import { join, dirname } from "node:path";
 import { existsSync } from "node:fs";
 import { fileURLToPath } from "node:url";
-import type { Task, TaskStore, MergeResult, AutomationStore } from "@kb/core";
+import type { Task, TaskStore, MergeResult, AutomationStore } from "@fusion/core";
 import type { AuthStorageLike, ModelRegistryLike } from "./routes.js";
 import { createApiRoutes } from "./routes.js";
 import { createSSE } from "./sse.js";