Extend Theme Config with Theme Presets

[rozd]

Extend the config to optionally include actual values:

 {
    "styles": {
      "colors": ["surface", "primary"]
    },
    "themes": {
      "default": {
        "colors": {
          "surface": { "light": "#FFFFFF", "dark": "#1C1C1E" },
          "primary": { "light": "#007AFF", "dark": "#0A84FF" }
        }
      },
      "forest": {
        "colors": {
          "surface": { "light": "#F5F5DC", "dark": "#2D3B2D" },
          "primary": { "light": "#228B22", "dark": "#90EE90" }
        }
      }
    }
  }

The generator would produce a fully populated Theme+Defaults.swift with static let default, static let forest, etc.

Thoughts

• makes more sense if theme presets come from another system or a design tool.
• switch between light/dark is must have, but runtime switching a whole theme is probably a rare use case.