[docs]chore: update theme colors and video quality

- Change color scheme from black/white to slate blue-gray
- Replace demo video with higher quality version (4.6MB)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/docs.json

@@ -3,9 +3,9 @@
   "theme": "mint",
   "name": "Actionbook",
   "colors": {
-    "primary": "#18181B",
-    "light": "#FAFAFA",
-    "dark": "#09090B"
+    "primary": "#475569",
+    "light": "#cbd5e1",
+    "dark": "#1e293b"
   },
   "favicon": "/favicon.ico",
   "navigation": {