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

package.json

@@ -6,7 +6,7 @@
   "packageManager": "pnpm@10.33.0",
   "scripts": {
     "dev": "tsx packages/cli/src/bin.ts",
-    "dev:ui": "pnpm --filter @kb/dashboard dev",
+    "dev:ui": "pnpm --filter @fusion/dashboard dev",
     "build": "pnpm -r build",
     "build:exe": "pnpm build && pnpm --filter @dustinbyrne/kb build:exe",
     "build:exe:all": "pnpm build && pnpm --filter @dustinbyrne/kb build:exe:all",