Unify weather providers into a single weather mode

[JanPetterMG]

This change consolidates all existing weather provider modes into a single unified Weather mode. The previous provider-specific modes have been deprecated and removed, while maintaining backward compatibility with existing configurations.

Key changes

Unified weather mode

• All 7 weather providers are now accessible through a single mode
• Provider selection is handled dynamically:
  • Web UI dropdown
  • Home Assistant integration
• Simplifies configuration and reduces mode fragmentation

Backward compatibility

• Existing configurations continue to work without breaking changes
• Legacy provider modes are deprecated and transparently mapped to the new system

Web UI improvements

• Visual overhaul of the weather interface
• New icons and refined presentation
• Temperature is now displayed alongside condition
• Minor UX enhancements and visual polish

Provider improvements

• Updated and standardized refresh intervals across providers
• Improved robustness and consistency
• Wttr.in:
  • Added support for an additional API format
  • Better resilience to upstream format changes

Documentation and CI

• Documentation updated to reflect the new unified mode
• CI workflows updated accordingly

Rationale

This refactor reduces duplication, simplifies the user experience, and provides a more maintainable architecture for future weather-related improvements.