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/app/utils/modelPresets.ts

@@ -1,4 +1,4 @@
-import type { ModelPreset } from "@kb/core";
+import type { ModelPreset } from "@fusion/core";
 
 export function getPresetByName(presets: ModelPreset[], name: string): ModelPreset | undefined {
   const normalizedName = name.trim().toLowerCase();