feat: Add llms.txt for AI crawler support

- Create website/llms.txt following llmstxt.org spec (H1, blockquote,
  H2 sections with link lists, Optional section)
- Include llms.txt in website build pipeline (generic files copy)
- Sections: Features, Download, Technical, Optional (alternatives,
  sitemap, privacy, imprint, join)

website/build.cjs

@@ -315,7 +315,7 @@ async function compile() {
     }
 
     // ── 5. Copy generic static files and verification files ──
-    const genericFiles = ['robots.txt', 'sitemap.xml', 'site.webmanifest', 'version.json'];
+    const genericFiles = ['robots.txt', 'sitemap.xml', 'site.webmanifest', 'version.json', 'llms.txt'];
     for (const file of genericFiles) {
         const src = path.join(websiteDir, file);
         const dest = path.join(wwwDir, file);

website/llms.txt

@@ -0,0 +1,33 @@
+# KoalaSync
+
+> Watch Netflix, YouTube, Twitch & any HTML5 video in perfect sync with friends. Free, open-source browser extension for Chrome and Firefox. No sign-up needed.
+
+KoalaSync is a privacy-first peer-to-peer video synchronization tool. It uses WebRTC for direct connections between peers — no video data ever passes through a server. The relay server is only used for signaling and optional room-based coordination. Self-hostable, MIT licensed.
+
+## Features
+
+- [Sync any HTML5 video](https://sync.koalastuff.net/): Works with Netflix, Emby, Jellyfin, YouTube, Twitch, Amazon Prime Video, Disney+, Crunchyroll, HBO Max and more
+- [Host & co-host controls](https://sync.koalastuff.net/#features): Synchronized play, pause, seek, host control mode, co-host roles
+- [Privacy-first](https://sync.koalastuff.net/#features): No accounts, no tracking, no data collection, peer-to-peer by design
+- [Available in 15 languages](https://sync.koalastuff.net/): English, Deutsch, Français, Español, Português, Italiano, Nederlands, Polski, Türkçe, Русский, 日本語, 한국어, 中文, Українська
+
+## Download
+
+- [Chrome Web Store](https://chromewebstore.google.com/detail/koalasync/obbnmkmlaaddodakcbdljknjpagklifc): Install KoalaSync for Chrome, Edge, and other Chromium-based browsers
+- [Firefox Add-ons](https://addons.mozilla.org/de/firefox/addon/koalasync/): Install KoalaSync for Firefox
+- [GitHub Releases](https://github.com/Shik3i/KoalaSync/releases): Manual download and release notes
+
+## Technical
+
+- [Source code](https://github.com/Shik3i/KoalaSync): Full MIT-licensed source on GitHub (extension, server, website)
+- [Changelog](https://github.com/Shik3i/KoalaSync/blob/main/docs/CHANGELOG.md): Version history and release notes
+- [Self-hosting guide](https://sync.koalastuff.net/#self-hosting): Run your own relay server
+- [Server](https://sync.koalastuff.net/): Node.js WebSocket relay, port 54000
+
+## Optional
+
+- [Alternatives hub](https://sync.koalastuff.net/alternatives/): Comparison with Teleparty, Scener, other sync tools
+- [Privacy policy](https://sync.koalastuff.net/privacy.html): Data handling and privacy information
+- [Imprint](https://sync.koalastuff.net/imprint.html): Legal notice
+- [Sitemap](https://sync.koalastuff.net/sitemap.xml): Full site index
+- [Join a room](https://sync.koalastuff.net/join.html): Direct room join page