feat: course website (Astro Starlight)

Pages (index, disclaimer, about), lockfile, root test:site script, fix for
Starlight 0.42 sidebar config and <details> rendering in generated MDX.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

site/src/content/docs/disclaimer.md

@@ -0,0 +1,13 @@
+---
+title: Disclaimer
+description: Trademarks, quoted card text and licensing.
+sidebar:
+  order: 1
+---
+
+This course is an independent, non-commercial educational project.
+
+- It is **not affiliated with or endorsed by Blizzard Entertainment or Hempuli**. Hearthstone is a trademark of Blizzard Entertainment. Baba Is You is a creation of Hempuli. All trademarks and game names belong to their respective owners.
+- Short card and rule texts are quoted for **educational commentary** on game design. No game assets, code or data from those games are included.
+- SpellGrid and all other course content are original.
+- The course is **free**, and released under the MIT license.