fix: add missing type exports for backwards compatibility

Added missing exports that existed in main:
- McpUiTheme, McpUiThemeSchema
- McpUiDisplayMode, McpUiDisplayModeSchema
- McpUiResourceCsp, McpUiResourceCspSchema
- McpUiResourceMeta, McpUiResourceMetaSchema

Also fixed theme/displayMode to match original values:
- theme: 'light' | 'dark' (removed 'system')
- displayMode: 'inline' | 'fullscreen' | 'pip' (removed 'carousel')

Verified: all 47 exports from main are preserved with compatible types.

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: ochafik