feat: Add tags page with post count display

[p-iknow]

Feature Description

Create a tags page that displays all blog post tags with their respective post counts, similar to: https://p-iknow.netlify.app/categories/

Requirements

• Create /tags/ page for both languages (/en/tags/, /ko/tags/)
• Display total number of tags
• List all tags with post count in parentheses
• Sort tags by post count (descending) or alphabetically
• Make tags clickable to filter posts by tag

Implementation Details

• Extract tags from all blog posts (frontmatter)
• Count posts per tag for each language separately
• Create responsive layout with Tailwind CSS
• Add TypeScript types for tag data structure
• Implement tag filtering functionality

Technical Tasks

• Create tags.astro page or [...slug].astro for tags
• Build tag collection logic in Astro
• Style tags list with hover effects (Tailwind)
• Add click handlers for tag filtering
• Ensure i18n support (separate tag counts per language)

UI/UX Requirements

• Clean, readable list layout
• Show "There are X tags" summary
• Consistent styling with blog theme
• Responsive design for mobile/desktop
• Hover effects and visual feedback

Acceptance Criteria

• Tags page displays all tags with accurate post counts
• Clicking a tag filters and shows related posts
• Works correctly for both English and Korean content
• Responsive and accessible design
• Fast loading and good performance

Reference

Similar layout to: https://p-iknow.netlify.app/categories/ (but using "tags" terminology)