fix: present not-found link as primary action

[janicduplessis]

Description

The not-found recovery link looked like inline text and was easy to overlook. It now uses the existing primary and inverse theme colors with spacing and radius tokens, and exposes an explicit button role and label while preserving its / destination and “Go to trails” copy.

Closes #6

Test plan

• Opened trailhead:///hackathon-missing-route on the iOS Stim simulator and verified the action changed from StaticText to Button with the label Go to trails.
• Checked the action in light and dark appearances for readable foreground and background colors.
• Pressed the action and verified it opened the Trails tab.

Before

After