fix(ui): prevent long toast messages from overflowing

[marcomarcogd]

Description

Keep toast notifications inside narrow application windows even when messages contain long continuous text.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• 🎨 Style/UI change
• ✅ Test addition/update

Related Issues

Fixes #1036

Changes Made

• Cap toast width to the available viewport.
• Allow long and unbroken messages to wrap inside the message region.
• Keep status icons and the close button visible without shrinking.
• Extend the existing frontend test file with a regression assertion.

Testing

Test Configuration

• OS: macOS 15
• MrRSS Version: current main
• Node Version: 24

Test Steps

1. Run cd frontend && npm run lint.
2. Run npm test -- --run src/App.test.ts -t 'keeps long toast messages inside narrow viewports'.
3. Verify a long continuous message wraps and the close button remains visible.

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing targeted tests pass locally with my changes
• This change has no dependent changes

Additional Notes

The existing broader App.test.ts mount test is affected locally by the Vitest environment not providing localStorage; the new targeted regression test passes independently.

Breaking Changes

None.