perf: ⚡ Slim down SolidElement base class to reduce bundle size

[AaronWeber90]

Current behavior

The SolidElement base class is inherited by all 59 components and includes several features that are only used by a handful of components:

• dir and lang reactive properties (unused by any component; native HTML attributes still work)
• token() method and animate.ts import (used by only 3 components: tag, video, audio)
• onThemeChange lifecycle hook (used by only 2 components: icon, audio)
• CSS @import for interactive.css, headline.css, paragraph.css (used by ~14 components)

This means every component carries the cost of these features in its bundle, even when unused.

Benefits

• Significantly reduced bundle size for consumers who import individual components
• Cleaner separation of concerns — features are opt-in rather than always included
• Better performance for end users

Technical Information

Removed rarely-used features from the SolidElement base class and moved them to opt-in modules:

• Removed dir and lang reactive properties
• Moved token() method and animate.ts import → standalone token() utility in src/internal/token.ts
• Moved onThemeChange lifecycle hook → self-managed listeners in the 2 consuming components (icon, audio)
• Moved CSS @import for interactive.css, headline.css, paragraph.css → importable modules in src/internal/shared-styles.ts (only added by the ~14 components that actually use them)
• Updated Storybook Vite config to process the new shared-styles.ts file with Tailwind

What remains in SolidElement:

• Tailwind --tw-* CSS variable resets (needed by all components)
• box-sizing reset and [hidden] rule
• emit() method (used by 20+ components)

DoR

• Item has business value
• Item has been estimated by the team
• Item is clear and well-defined
• Item dependencies have been identified

DoD

• Documentation has been created/updated (if applicable)
• Migration Guide has been created/updated (if applicable)
• Relevant E2E tests (Features, A11y, Bug fixes) are created/updated
• Relevant stories (Features, A11y) are created/updated
• Implementation works successfully on feature branch