fix: improve toast notification consistency across screen sizes

the firehose toast notification now behaves consistently on both desktop and mobile:
- uses max-width: min(300px, calc(100vw - 2rem)) to respect both size limit and viewport
- width: max-content keeps toast compact, only as wide as needed
- removed mobile-specific left/right/max-width overrides that caused full-width stretch
- toast remains right-aligned and compact on all screen sizes

before: mobile toast spanned entire screen width, looked oversized
after: mobile toast is same compact size as desktop, just positioned lower to avoid button overlap

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>