fix(web): move docs CSS import from layer(components) to layer(legacy)

The docs package variables.css sets --background-color: #ffffff in
:where(:root) inside layer(components). Because CSS layer ordering
beats specificity, this always overrode the dark mode variables in
layer(legacy), making the page background permanently white.

Moving the import to layer(legacy) restores normal specificity-based
cascade where [data-theme="dark"] correctly overrides :where(:root).

Author: Movm

apps/web/src/assets/styles/index.css

@@ -50,8 +50,13 @@
 /* ── Chat package component styles (merges into Tailwind's components layer) ── */
 @import "../../../../../packages/chat/src/styles/chat-embedded.css" layer(components);
 
-/* ── Docs package component styles (BlockNote theme overrides) ── */
-@import "../../../../../packages/docs/src/styles/docs.css" layer(components);
+/* ── Docs package default variables + BlockNote theme overrides ──
+   Imported into layer(legacy) so its :where(:root) defaults don't
+   override dark-mode variables — layer(components) would win over
+   layer(legacy) regardless of selector specificity. BlockNote
+   component-level overrides still work because they target specific
+   .bn-* selectors with higher specificity than the :where() defaults. */
+@import "../../../../../packages/docs/src/styles/docs.css" layer(legacy);
 
 /*
  * Source paths for Tailwind class detection