feat(cli): refactor embedded assets with Bun-specific and stub implementations

Split embedded assets loading into runtime-specific variants using package.json imports field. Bun-compiled binaries use the full implementation with file assets, while stub fallback provides clear error for non-Bun runtimes.

cli/src/types/bunBundle.d.ts

@@ -8,4 +8,6 @@ declare module 'bun:bundle' {
             | 'HAPI_TARGET_WIN32_X64'
             | 'HAPI_TARGET_WIN32_ARM64';
     }
+
+    export function feature(name: Registry['features']): boolean;
 }