Phase 7: browser-side spell check (nspell, en-US)

Vendored Hunspell en.aff/en.dic into web/public/dictionaries/en/ (served as a
static asset + embedded in the binary, kept out of the JS bundle). dictionary-en
moved to a devDep — only used to source the files.

- useSpellChecker (App-level, loads once/session): fetches the dict, builds an
  nspell instance, replays a localStorage personal word list; addWord persists
  and bumps a version so consumers re-decorate. Ambient types in
  src/types/nspell.d.ts (the package ships none).
- SpellCheck Tiptap extension: misspellings as ProseMirror decorations (no
  stored marks), recomputed on edit / caret move / checker swap. Latin-only
  tokenizer so CJK is never flagged; skips short tokens + all-caps acronyms;
  exempts the caret word to avoid mid-typing jitter. Reuses mapOffset (now
  exported from SuggestionHighlight); wordAt resolves the exact span on click.
- MisspellCard: soft rose wavy underline, bilingual popover with up to 5 nspell
  corrections (click to replace) + add-to-dictionary. Closes on outside-pointer,
  edit, or doc switch.

Chinese spell check intentionally omitted — nspell is dictionary-based and
English-only; Chinese typos (homophone 别字) need an LLM, out of v1 scope.

tsc/vite/go build+vet clean; live server serves both dict files; nspell
behavior smoke-tested.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/src/index.css

@@ -136,6 +136,26 @@ button, a, input {
   animation: petal-suggestion-in 200ms ease both;
 }
 
+/* --- Spell check ------------------------------------------------------------
+   Browser-side nspell flags misspellings with a soft rose wavy underline (a
+   gentler take on the classic red squiggle, to fit the pastel palette). Like the
+   suggestion layer these are ProseMirror decorations, never stored marks.
+   Clicking a flagged word opens its MisspellCard with corrections. */
+.petal-misspelling {
+  cursor: pointer;
+  text-decoration: underline wavy var(--color-accent);
+  text-decoration-skip-ink: none;
+  text-underline-offset: 2px;
+}
+.petal-misspelling:hover {
+  background: var(--color-surface-alt);
+  border-radius: 2px;
+}
+
+.petal-misspell-card {
+  animation: petal-suggestion-in 200ms ease both;
+}
+
 /* --- Accept confetti --------------------------------------------------------
    A tiny CSS-only burst played where a suggestion is accepted: four colored
    dots spray up-and-out, then fade. No JS animation — each dot reads its