fix(desktop): hide helper process windows - #40137

Summary

• Set windowsHide for remaining TUI native helper subprocesses (clipboard/editor)
• Add a shared desktop main-process helper for hidden subprocess windows
• Use it for app lookup and custom open-path launches

Fixes #31629

Test Plan

• bun test test/clipboard.test.ts test/editor.test.ts
• bun test src/main/apps.test.ts src/main/process-options.test.ts
• bun run typecheck (packages/tui)
• bun run lint packages/tui/src/clipboard.ts packages/tui/test/clipboard.test.ts packages/tui/src/editor.ts packages/tui/test/editor.test.ts packages/desktop/src/main/apps.ts packages/desktop/src/main/apps.test.ts packages/desktop/src/main/process-options.ts packages/desktop/src/main/process-options.test.ts packages/desktop/src/main/ipc.ts
• git diff --cached --check
• staged secret scan

Note: bun run typecheck from packages/desktop is blocked in this Windows checkout by the existing packages/app/src/custom-elements.d.ts symlink placeholder being materialized as the literal text ../../ui/src/custom-elements.d.ts.