Add import-from-image URL flow for custom puzzles

[NickTheDevOpsGuy]

Summary

The roadmap already calls out puzzle import from URL. Bring that back as a polished flow so players can create puzzles from images they find online.

Why this matters

• Huge replay value.
• Lets players bring their own content into the app.
• Creates strong shareability and creator energy.

Scope

• Add a guided URL import flow with validation.
• Show a preview before starting the puzzle.
• Handle invalid URLs and failed image loads gracefully.
• Keep the existing staged modal flow feeling intentional.

Acceptance Criteria

• A player can paste an image URL and start a puzzle from it.
• Broken URLs and unsupported images show helpful errors.
• The imported puzzle works with existing play modes and completion flows.
• The flow feels mobile-friendly and does not require a desktop-only interaction.

Bucket

Big swing