Complete "Entering / exiting fullscreen" pattern documentation

Add `App_onhostcontextchanged_respondToDisplayMode` example showing how to
listen for display mode changes and update UI with `classList.toggle()`.

Update `App_requestDisplayMode_fullscreen` to `App_requestDisplayMode_toggle`
to show the common toggle pattern checking `availableDisplayModes` first.

Refactor full examples (pdf-server, shadertoy-server) to use
`classList.toggle(class, condition)` instead of add/remove branches.

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

docs/patterns.md

@@ -43,9 +43,15 @@ Use the SDK's style helpers to apply host styling, then reference them in your C
 
 {@includeCode ./patterns.tsx#hostStylingReact}
 
-## [TODO] Support fullscreen / exit fullscreen
+## Entering / Exiting fullscreen
 
-{@includeCode ./patterns.tsx#fullscreen}
+Toggle fullscreen mode by calling {@link app!App.requestDisplayMode requestDisplayMode}:
+
+{@includeCode ../src/app.examples.ts#App_requestDisplayMode_toggle}
+
+Listen for display mode changes via {@link app!App.onhostcontextchanged onhostcontextchanged} to update your UI:
+
+{@includeCode ../src/app.examples.ts#App_onhostcontextchanged_respondToDisplayMode}
 
 ## [TODO] Persist data (incl. widget state)
 

docs/patterns.tsx

@@ -97,15 +97,6 @@ function hostStylingReact() {
   //#endregion hostStylingReact
 }
 
-/**
- * Example: Support fullscreen / exit fullscreen
- */
-function fullscreen() {
-  //#region fullscreen
-  // TODO: Implement fullscreen support
-  //#endregion fullscreen
-}
-
 /**
  * Example: Persist data (incl. widget state)
  */
@@ -155,7 +146,6 @@ void authenticatedCalls;
 void errorsToModel;
 void hostStylingVanillaJs;
 void hostStylingReact;
-void fullscreen;
 void persistData;
 void lowerPerceivedLatency;
 void iframeAndMcpApps;