Implement tag/category filtering

[github-actions]

Tag System

Primary Categories:

• AI
• Security
• Architecture
• Development

Implementation

• Tag buttons/pills at top of blog page
• Filter posts by selected tag
• Show post count per tag
• "All Posts" option to clear filter

Acceptance Criteria

• Tags visible on blog index
• Clicking tag filters posts
• URL updates with filter (optional)
• Clear filter option available
• Mobile responsive

Estimated Time: 2 hours