feat(ui): add icon picker, color picker and provider icon components

Implement comprehensive icon selection system for provider customization:

## New Components

### ProviderIcon (src/components/ProviderIcon.tsx)
- Render SVG icons by name with automatic fallback
- Display provider initials when icon not found
- Support custom sizing via size prop
- Use dangerouslySetInnerHTML for inline SVG rendering

### IconPicker (src/components/IconPicker.tsx)
- Grid-based icon selection with visual preview
- Real-time search filtering by name and keywords
- Integration with icon metadata for display names
- Responsive grid layout (6-10 columns based on screen)

### ColorPicker (src/components/ColorPicker.tsx)
- 12 preset colors for quick selection
- Native color input for custom color picking
- Hex input field for precise color entry
- Visual feedback for selected color state

## Icon Assets (src/icons/extracted/)
- 38 high-quality SVG icons for AI providers and platforms
- Includes: OpenAI, Claude, DeepSeek, Qwen, Kimi, Gemini, etc.
- Cloud platforms: AWS, Azure, Google Cloud, Cloudflare
- Auto-generated index.ts with getIcon/hasIcon helpers
- Metadata system with searchable keywords per icon

## Build Scripts
- scripts/extract-icons.js: Extract icons from simple-icons
- scripts/generate-icon-index.js: Generate TypeScript index file

src/icons/extracted/github.svg

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