fix: prevent GalleryDetail browser-open crash in TUI

[cursor]

Summary

• fixes a critical crash path in GalleryDetail introduced by the [o] open in browser action
• wraps the open(...) call in a handled promise (void ... .catch(...)) instead of firing an unhandled async rejection
• surfaces a user-facing error (Failed to open browser or underlying message) in the existing error state

Critical bug

When the user presses [o] in gallery detail and the system opener fails (e.g. no desktop opener, missing xdg-open, headless environment), open() rejects. The previous code invoked open(...) without await/.catch(), creating an unhandled promise rejection from an input handler. On modern Node runtimes this can terminate the process, crashing the TUI.

Validation

• pnpm typecheck passes
• pnpm build && pnpm test passes (29 tests)
• verified no behavioral change to successful open path