Theme Engine: ref() token references not resolved in ejected CSS

Bug Description

The ref() helper function in @theme-engine/helpers/define-theme creates token references (e.g., $global.primaryColor) that are not properly resolved when generating static CSS via the eject CLI.

Expected Behavior

When using ref() to reference another token:

tokens: {
  'global.primaryColor': '#D49653',
  'tooltip.bg': ref('global.primaryColor'),  // Creates '$global.primaryColor'
}

The ejected CSS should output either:

1. Resolved value: --tooltip-bg: #D49653;
2. CSS var reference: --tooltip-bg: var(--global-primaryColor);

Actual Behavior

The ejected CSS outputs the raw reference string, which is invalid CSS:

--tooltip-bg: $global.primaryColor;

Root Cause

The BaseResolver.handleCheckExplicit() method in engine/core/base-resolver.ts:210-226 returns explicit values as-is without checking if they are $tokenPath references that need further resolution:

protected handleCheckExplicit(ctx: ResolutionContext<TValue>, frame: ResolutionFrame): void {
  const explicitValue = ctx.values[frame.path];
  if (explicitValue !== null && explicitValue !== undefined) {
    // Returns value as-is, even if it's a '$...' reference
    ctx.results.set(frame.path, explicitValue);
    ctx.stack.pop();
    return;
  }
  // ...
}

The CSS generator in engine/eject/generate-css.ts:72 also outputs values without transformation:

lines.push(`${indent}${cssVarName}: ${value};${newline}`);

Steps to Reproduce

1. Create a theme using ref():

import { defineTheme, ref } from '../engine/helpers/define-theme';

export default defineTheme({
  $meta: { id: 'test', name: 'Test', version: '1.0.0' },
  tokens: {
    'global.primaryColor': '#D49653',
    'tooltip.bg': ref('global.primaryColor'),
  },
  behaviors: {},
});

1. Run the eject CLI:

npx tsx packages/theme-engine/cli/eject.ts -t path/to/theme.ts -o /tmp/test

1. Check the output CSS - it contains $global.primaryColor instead of a valid value.

Affected Files

• packages/theme-engine/engine/core/base-resolver.ts - Resolver doesn't expand $ references
• packages/theme-engine/engine/eject/generate-css.ts - CSS generator doesn't transform $ to var()
• packages/theme-engine/engine/helpers/define-theme.ts - Documents ref() but feature is incomplete

Suggested Fix Options

Option A: Resolve at build time

Modify the resolver to detect $tokenPath values and resolve them to concrete values by looking up the referenced token.

Option B: Convert to CSS var()

Modify the CSS generator to transform $token.path → var(--token-path) for runtime resolution.

Option C: Hybrid approach

• For eject (static CSS): Resolve to concrete values
• For runtime: Convert to CSS var() references

Workaround

Until fixed, avoid using ref() and instead:

1. Rely on fallback chains (which work correctly)
2. Use hardcoded values for tokens without applicable fallbacks

Environment

• Package: @theme-engine
• File: packages/theme-engine/themes/stunning.theme.ts