feat: April Fools fake math-themed ads

[devin-ai-integration]

Summary

Adds fake math-themed banner ads to the homepage for April Fools Day. Includes:

• 6 inline banner ads (728×200px images) injected between content sections via JS with staggered delays (1.5–4s), causing intentional layout shift (no reserved height)
• 2 sidebar skyscraper ads (160×600px) fixed-positioned in the blank space flanking the content column, visible only on xl (≥1280px) viewports
• Spinning Tux penguin fixed in the bottom-right corner, rotating continuously. Clicking it alerts "🐧 I use Arch btw"
• All ads show an "April Fools! 🤡" alert when clicked
• A new {% block sidebar_ads %} hook in base.html (only overridden on the homepage)

Ad lineup (each with a distinct visual style):

1. MathCoin — yellow popup/alert style with dashed red border, centered layout
2. TI-84 Plus CE Quantum Edition — 90s Geocities style with tiled star background, visitor counter, webring footer
3. MATHLETE Protein Powder — infomercial/QVC style with "CALL NOW 1-800-MATH-BRO" panel, white background
4. Proof by Intimidation: The Masterclass — dark academia course platform style with hero headshot, pricing sidebar
5. Euler's Identity Cologne by Calvin Kℂlein — newspaper classified ad style with cream background, serif typography
6. Wolfram|Alpha Ultra Premium+ Platinum — fake browser toolbar/download style with green download button and progress bar

Updates since last revision

• Redesigned all 6 inline banner ads to have much more visual variety — each ad now has a completely different layout, color scheme, and aesthetic rather than sharing the same left-text/right-icon gradient template

Review & Testing Checklist for Human

• Verify the new ad images look correct — the ads were regenerated as PNGs via Playwright; confirm each one renders properly and looks intentionally sloppy/distinct from the others
• Verify visual appearance at different viewport widths — sidebar ads use calc((100vw - 896px) / 2 - 180px) which hardcodes the max-w-4xl (896px) content width. Check that sidebars don't overlap content on viewports between 1280–1440px
• Check the extra <hr> elements — ads 3–6 each add an <hr> above them. Before those ads load in (during the 2–4s delays), the page will show several consecutive horizontal rules with nothing between them. Decide if this is acceptable
• Mobile layout — sidebar ads are hidden below xl, but confirm the inline ads don't break the layout on small screens (they're 100% width, max 728px)
• z-index conflicts — spinning Tux is z-index: 9999, sidebar ads are z-index: 40, mobile menu is z-50. Verify Tux doesn't cover the mobile hamburger menu
• Plan for removal — there is no date-gating; these ads will show indefinitely until this commit is reverted. Consider whether you want to add a date check or just revert the PR after April 1

Recommended test plan: deploy to a preview environment, open the homepage on both a narrow (mobile) and wide (≥1440px) viewport, wait ~5s for all ads to load, scroll the full page, click a few ads and the Tux to confirm alerts fire.

Notes

• Tux PNG sourced from Wikimedia Commons (Larry Ewing's Tux, freely licensed)
• Ad banner images were generated by rendering HTML templates to PNG via Playwright (source HTML files not committed)
• Requested by: @oliver-ni
• Devin session: https://app.devin.ai/sessions/942b88366ae34f649f6524bf55f7d55f

[devin-ai-integration]

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