chore: migrating codebase to typescript

[Hannahbird]

Summary

Migrated the entire component library from JavaScript to TypeScript, improving type safety and developer experience for consumers.

Changes

TypeScript Migration

• Converted all 6 components to TypeScript (.js → .ts)
• Added comprehensive type definitions and interfaces for all components
• Configured tsconfig.json with Lit-optimized settings
• Added type checking scripts (typecheck, typecheck:watch)

Build & Distribution Updates

• Updated build process to compile TypeScript (npm run build)
• Changed distribution to emit compiled .js files with .d.ts type declarations
• Updated package.json exports to point to dist/ directory
• Added prepublishOnly script to ensure build runs before publishing

Type Definitions Added

• DataTableColumn, RowData interfaces for data-table component
• ToggleChangedDetail interface for toggle-switch component
• ActionMenuItem, ResourceData interfaces for action-menu component
• ButtonProps, HeaderProps interfaces for Storybook components

Developer Experience

• Consumers now get full IntelliSense and type checking when using the library
• Backward compatibility maintained - no breaking changes to component APIs
• Better IDE support with autocomplete and inline documentation

Testing

• ✅ TypeScript compilation passes with 0 errors
• ✅ All components build successfully
• ✅ Storybook stories updated and working

Version

Bumped to v1.4.1 (minor version for feature addition)

[Hannahbird]

You can test the implementation on Epinio in this PR epinio/ui#485

[dcharles525]

LGTM