[Hackathon demo] Include visible trail stats in each card accessibility label

Hackathon demo ticket. This is intentionally small and self-contained.

## Problem

Trail cards show distance, ascent, and estimated duration, but their accessibility label only names the trail, region, difficulty, and rating.

## Scope

Update the accessible name assembled in src/components/TrailCard.tsx. Reuse the same formatted values already shown by the card.

## Acceptance criteria

- A trail card accessibility label includes distance, ascent, and estimated duration.
- Values respect the current metric or imperial setting.
- Visible card content and navigation behavior stay unchanged.

## Validation

Follow docs/mobile-agent-loop.md.

Before: capture the Trails screen and the agent-device attributes for one named card.

After: use the same card and settings, prove the expanded label with agent-device, and capture the matching screen.

The PR description must include clearly labeled Before and After evidence.