Refine appearance settings and syntax highlighting

Keep parsed chat and tool detail content in sync with appearance token changes. Hide font-family controls on native, use One as the default syntax theme, add Swift highlighting, and give Nord a distinct light palette.

docs/unistyles.md

@@ -301,6 +301,7 @@ Gotchas:
 - **Narrow the discriminated union before spreading.** `updateTheme`'s updater returns the theme union; spreading the union widens `colorScheme` to `"light" | "dark"`, which is assignable to neither concrete member. Branch on `t.colorScheme` so each branch spreads a single narrowed theme type (no `as`).
 - **`lineHeight.diff` is the code/diff line-height axis** — it is coupled to the code-font-size control (≈ `codeFontSize * 1.5`). Do NOT use it for prose. Markdown body line-height scales with the UI ramp (`Math.round(theme.fontSize.base * 1.4)`); routing prose through `lineHeight.diff` clips text at small code sizes.
 - **High-churn draft values** (live-while-typing in the appearance preview) bypass the theme: apply them as inline styles marked with `inlineUnistylesStyle` so per-keystroke values don't grow the `#unistyles-web` CSS registry.
+- **Mounted parsed content uses `AppearanceStyleBoundary`.** Markdown, syntax-highlighted code, and tool-call detail bodies can contain memoized/custom renderer trees that do not naturally re-run when runtime-patched appearance tokens change. Wrap the parsed surface once with `packages/app/src/components/appearance-style-boundary.tsx`; do not add local "appearance key" props at each callsite.
 - **Dynamic font tokens stay widened.** `fontFamily`, `fontSize`, and `lineHeight` on `commonTheme` are annotated `string`/`number` (not narrowed by `as const`) so the updater's return assigns; the platform default stacks live in `DEFAULT_UI_FONT_STACK` / `DEFAULT_MONO_FONT_STACK`.
 
 ## Debugging