Add stock picture selection when creating rental items

[Rotorsoft]

Summary

• Add stock picture selection UI when creating rental items, featuring a responsive grid of 10 curated equipment images with animated hover effects and selection states using brand colors
• Extend domain model to support imageUrl field in state schema, ItemCreated event, and CreateItem action following the existing event sourcing pattern
• Display selected images in item details view (full-size with styled container) and inventory list (thumbnails), with graceful fallback styling for items without images

Test Plan

• Verify domain unit tests pass: imageUrl is correctly stored in state after CreateItem action
• Verify API integration tests pass: createItem mutation accepts and returns imageUrl
• Manually test picture picker displays grid of stock images with hover animations
• Confirm selected picture shows visual indicator (purple border, checkmark overlay)
• Verify selected image appears in item details page after creation
• Check thumbnails display correctly in inventory list
• Confirm items without images show appropriate placeholder styling
• Run full test suite: pnpm test

Closes #1

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Created with Claude by gent