fix: prevent GalleryDetail browser-open failures from crashing TUI

[cursor]

Summary

• fixes a high-severity TUI crash path introduced by the gallery "open in browser" behavior
• wraps the async browser launch in a safe helper that catches launch failures and returns a typed result
• updates GalleryDetail to handle failures by surfacing an error message instead of allowing an unhandled rejection
• adds focused unit tests for success, Error rejection, and non-Error rejection paths

Bug and impact

Pressing o in gallery detail triggered open(...) without await or .catch(...). If browser launch fails (for example, missing/broken opener on headless/minimal environments), the promise rejects unhandled. In Node 22, unhandled rejections terminate the process, causing immediate TUI exit (significant user-facing breakage in a critical interaction path).

Root cause

A behavioral change switched gallery detail from synchronous navigation to async browser launch, but the new async call was fire-and-forget with no rejection handling.

Fix

• Added safeOpen helper (src/core/safe-open.ts) to contain and normalize browser-launch errors.
• Updated src/screens/GalleryDetail.tsx to call safeOpen and set screen error state on failure.
• Added src/core/safe-open.test.ts to lock in rejection handling behavior.

Validation

• pnpm test src/core/safe-open.test.ts ✅
• pnpm typecheck ✅