feat(editor): spell & grammar checking (Chunk #7)

Offline spellcheck via hunspell compiled to WASM (runs fully in-browser),
plus optional self-hostable LanguageTool grammar/style checking.

- hunspell-wasm spell engine with bundled en_US dictionary (base64-decoded
  browser-safe via atob + TextDecoder)
- LanguageTool engine (self-hostable, docker compose snippet under
  docker/languagetool/)
- single decoration pipeline: spell + grammar hits merge into one squiggle
  layer (red=spelling, blue=grammar) with a side panel to jump/apply/ignore
  and add-to-dictionary
- useCheckService hook wired into WritingView; check.css loaded in main.tsx
- spell + grammar unit tests (30 editor tests green)

PLAN.md and CHUNK#7.md updated to reflect completion.

apps/web/src/store/settings.ts

@@ -18,6 +18,8 @@ export function fontFamilyCss(value: FontFamily): string {
   return found?.css ?? FONT_FAMILIES.at(0)?.css ?? "";
 }
 
+export type GrammarProvider = "local" | "languagetool";
+
 export interface AppSettings {
   theme: ThemeId;
   accentColor: string;
@@ -31,6 +33,12 @@ export interface AppSettings {
   autoSave: boolean;
   focusMode: boolean;
   typewriterMode: boolean;
+  // Spell & grammar (Chunk #7)
+  enableSpellcheck: boolean;
+  enableGrammarCheck: boolean;
+  spellcheckLanguage: string;
+  grammarProvider: GrammarProvider;
+  grammarApiKey: string;
 }
 
 export const DEFAULT_SETTINGS: AppSettings = {
@@ -46,6 +54,12 @@ export const DEFAULT_SETTINGS: AppSettings = {
   autoSave: true,
   focusMode: false,
   typewriterMode: false,
+  // Spell & grammar (Chunk #7)
+  enableSpellcheck: true,
+  enableGrammarCheck: false,
+  spellcheckLanguage: "en_US",
+  grammarProvider: "local",
+  grammarApiKey: "",
 };
 
 const STORAGE_KEY = "pubscript.settings.v1";