Add 404 page

[replakcan]

Description

Create a custom 404 page for unknown routes.

Scope

• Add 404/not-found page
• Include helpful message
• Add link back to home page
• Match site layout

Out of Scope

• Advanced error tracking
• Search suggestions
• Backend error pages

Acceptance Criteria

• Custom 404 page exists
• Page matches site layout
• Page includes link to home
• Page is responsive
• npm run build succeeds

Technical Notes

• Must work with static export and CloudFront behavior.

Related

• Related to: Create base layout