Feat: spell check toggle for desktop (#626)

* feat: (desktop) add spellcheck toggle for text inputs

* fix: show spellcheck toggle only on desktop

* fix: apply the preference consistently to chat and commit inputs

packages/ui/src/lib/desktop.ts

@@ -116,6 +116,7 @@ export type DesktopSettings = {
   gitModelId?: string;
   pwaAppName?: string;
   toolCallExpansion?: 'collapsed' | 'activity' | 'detailed' | 'changes';
+  inputSpellcheckEnabled?: boolean;
   userMessageRenderingMode?: 'markdown' | 'plain';
   stickyUserHeader?: boolean;
   fontSize?: number;