Add Facebook and Messenger buttons to hero section

[Second-penguin-planning]

Motivation

• Add visible social CTAs in the hero area so visitors can quickly access the Facebook page and Messenger as requested, using the provided link https://www.facebook.com/second.penguin/.

Description

• Inserted a new div block hero-social-buttons in index.html containing two stacked anchors for Facebook and Messenger that both point to https://www.facebook.com/second.penguin/ and include accessible attributes (target="_blank" and rel="noopener noreferrer").
• Updated css/style.css to set .hero to position: relative and added .hero-social-buttons / .hero-social-button styles for bottom-right positioning, colors, hover effects and a mobile fallback where the buttons flow under the hero content.
• Removed the old site-wide fixed SNS block (.sns-fixed) from index.html so social links are consolidated inside the hero section.

Testing

• Ran git diff --check to ensure no whitespace errors and it passed.
• Launched a local server with python -m http.server 8000 and opened http://127.0.0.1:8000/index.html to validate the changes render.
• Used Playwright to capture a screenshot (artifacts/hero-social-buttons.png) of the updated hero to visually verify placement and styling (screenshot capture succeeded).

---

Codex Task