[FEAT] Admin customization: themes, titles, and branding

[BenGWeeks]

Problem

Currently, Diagon Alley has a fixed appearance and branding. LNbits admins who deploy their own instance may want to customize the marketplace to match their branding or community.

Proposed Solution

Allow admins to customize various aspects of their Diagon Alley instance:

Customizable Elements

Branding

• Marketplace title (e.g., "My Community Market" instead of "Diagon Alley")
• Logo/icon
• Tagline/subtitle
• Footer text

Theming

• Color scheme (primary, secondary, accent colors)
• Dark/light mode default
• Custom CSS overrides

Layout

• Show/hide banner image
• Default view (grid vs list)
• Categories to display
• Featured merchants section

Implementation Ideas

• Admin settings page within LNbits extension
• Store configuration in database
• CSS variables for easy theming
• Template overrides for advanced customization

Benefits

• White-label marketplace deployments
• Community-specific branding
• Better integration with existing LNbits themes
• Flexibility for different use cases (local markets, niche communities, etc.)