Add sidebar ads for The Vibes and Masterclass

[simonhamp]

Summary

• Adds a The Vibes sidebar ad with the event photo as a softened background image, linking to /the-vibes with "Only 100 tickets!" label
• Adds a The Masterclass sidebar ad with emerald/teal gradient and academic cap icon, linking to /course with "Early Bird Pricing" label
• Both new ads are included in the default rotation (blog, article pages) and in the docs sidebar

Test plan

• Visit /blog and refresh several times to see all 5 ads rotate
• Visit a blog article page and verify ads appear in the sidebar
• Visit /docs/mobile and /docs/desktop and verify new ads appear in the sidebar rotation
• Verify The Vibes ad links to /the-vibes
• Verify The Masterclass ad links to /course
• Check mobile viewport fallback ads render correctly

🤖 Generated with Claude Code