Add custom scenario creation controls and Sail branding modal

[snowsecure]

Summary

• add UI to switch between suggested scenarios and custom roleplay setups with full detail inputs
• build custom scenarios in the app with validation, reset handling, and consistent difficulty selection
• centralize custom scenario typing for reuse
• replace sailboat image with an emoji-powered Sail badge and modal contact card for Stewart AI Lab
• move custom scenario inputs into a dedicated modal triggered from the Custom selector for a cleaner layout
• ensure the Custom button always opens the modal rather than leaving the form inline

Testing

• npm run lint

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Codex Task