Complete "Support native host styling using CSS variables" pattern documentation

References existing type-checked examples instead of a stub:
- Vanilla JS: `applyHostStyleVariables_fromHostContext` from `src/styles.examples.ts`
- React: `useHostStyles_basicUsage` from `src/react/useHostStyles.examples.tsx`

Expanded `applyHostStyleVariables_fromHostContext` to show the full pattern:
using CSS variables in styles, applying on `onhostcontextchanged`, and
applying initial styles after `connect()`.

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

docs/patterns.ts

@@ -31,15 +31,6 @@ function errorsToModel(app: App) {
   //#endregion errorsToModel
 }
 
-/**
- * Example: Support native host styling / use CSS variables
- */
-function hostStyling() {
-  //#region hostStyling
-  // TODO: Implement host styling support via CSS variables
-  //#endregion hostStyling
-}
-
 /**
  * Example: Reacting to light/dark theme changes
  */
@@ -112,7 +103,6 @@ function migrateFromOpenai() {
 // Suppress unused variable warnings
 void authenticatedCalls;
 void errorsToModel;
-void hostStyling;
 void lightDarkTheme;
 void fullscreen;
 void persistData;