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/cli/tsup.config.ts

@@ -12,7 +12,7 @@ export default defineConfig({
   format: ["esm"],
   platform: "node",
   target: "node22",
-  noExternal: [/^@kb\//],
+  noExternal: [/^@fusion\//],
   splitting: false,
   clean: true,
   onSuccess: async () => {