Implement rich text editor for blog posts

[jhash]

Summary

• Integrated Rails Action Text to enable rich text editing for blog post content
• Migrated from plain text content field to Action Text rich content
• Updated all views and controllers to support rich text display and editing

Changes

• Added Action Text to the BlogPost model using has_rich_text :content
• Removed the plain text content column from the blog_posts table
• Updated the blog post form to use rich_text_area for content editing
• Modified all blog post views (public and admin) to properly render rich text content
• Updated RSS and Atom feeds to handle Action Text content properly
• Fixed admin search functionality to work with Action Text content
• Resolved all rubocop style issues

Test Plan

• Create a new blog post with rich text formatting (bold, italic, links, images)
• Verify rich text displays correctly on the public blog post page
• Verify rich text displays correctly on the admin blog post show page
• Test editing an existing blog post with rich text
• Confirm RSS and Atom feeds work correctly
• Test admin search functionality for content within blog posts

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