New documentation hub at /docs

We have consolidated our guides into a single documentation hub.

What's new:

• /docs — a new hub page linking to every guide
• /docs/embed-guide — a new, complete guide to embedding and sharing tours, videos, and photos: iframe snippets, oEmbed auto-embed, QR codes, and platform-specific instructions for WordPress, Wix, Squarespace, Notion, and more
• /docs/video-formats — a new guide explaining why 360° MP4 files are special: equirectangular projection, spherical metadata, and supported codecs
• The existing How-To guide and FAQ moved to /docs/how-to and /docs/faq (old links still work and redirect automatically)