Add appearance settings for theme, fonts, and syntax highlighting (#1236)

* Add appearance settings for theme, fonts, and syntax highlighting

New Appearance section in Settings to configure the app theme, UI and
mono font family + size, and a syntax-highlighting theme chosen
independently of light/dark. Font family fields default to empty and
show the active system stack as the placeholder; a live split-diff
preview reflects the choices as they change. The theme picker moves
here from General.

Preferences are client-only (AsyncStorage) and applied at runtime by
patching every registered Unistyles theme via
UnistylesRuntime.updateTheme, so existing StyleSheet consumers repaint
with no per-component preference reads and no useUnistyles. No
daemon/protocol change.

* Expand syntax themes and move the preview under the chooser

Replace the small fixed syntax-theme set with eight popular themes — GitHub,
Catppuccin, Dracula, Tokyo Night, One, Nord, Gruvbox, Solarized — built from a
compact per-theme role palette. The app theme and syntax theme stay separate;
the only coupling is the light/dark axis: a theme with both variants uses its
light palette on a light app and its dark palette on a dark app, while the code
frame (gutter, line numbers, background) keeps following the app theme. Default
is now GitHub (GitHub keeps its existing hand-tuned maps for an exact match).

Move the live preview directly under the syntax-theme chooser, drop the
"preview.ts" filename header, and use a clearer code snippet for it.

* Update settings e2e for the moved theme picker and Appearance section

The theme picker moved from General to the new Appearance section, so the
General-content assertion no longer finds "Theme" — point it at "Default send"
(which stays in General) and add Appearance to the e2e section map plus an
expectAppearanceContent check, and exercise the Appearance section in the
sidebar-navigation test.

* Render the appearance preview as a unified diff

Switch the live preview from side-by-side columns to a single unified diff:
unchanged context lines plus "-"/"+" rows for the change, matching how diffs
read elsewhere in the app. Same snippet, mono font, syntax colors, and live
code-font draft behavior.

* Fix code font size change shrinking all UI text

applyAppearance scaled the live (already-patched) theme ramp instead of the
authored FONT_SIZE ramp, so it was not idempotent: every appearance change
re-scaled the current sizes, compounding the whole-UI font scale. With any
non-default UI size, changing the code size — or any setting — shrank (or grew)
all app text, and it persisted into the theme. Build the ramp from the canonical
FONT_SIZE ramp each apply (code size still set absolutely), so applies are
idempotent and a code-size change never touches the UI ramp.

* Apply the interface font across the app on web

react-native-web stamps a default font onto every text element, so the interface
font only reached the few components that set a font explicitly. Inject one rule
that points all text at a CSS variable (updated live as the setting changes),
with high specificity (1,2,0) so it deterministically beats RN-web's base font
and Unistyles' generated classes — no stylesheet-order fragility. Code, diff, and
monospace surfaces carry a `data-pmono` marker (and their subtrees are excluded),
so they keep their code font.

Web-only: React Native has no global font cascade, so native still applies the UI
font only where components opt in. Inline `code` within chat prose is a known
minor gap (its render paths aren't tagged yet).

* Keep preview code in the code font

* Apply code font settings to terminals

* Fix settings host picker import after rebase

* Format terminal webview bundle

packages/app/src/hooks/use-settings/index.ts

@@ -14,12 +14,20 @@ import {
   APP_SETTINGS_QUERY_KEY,
   DEFAULT_APP_SETTINGS,
   DEFAULT_CLIENT_SETTINGS,
+  DEFAULT_CODE_FONT_SIZE,
   DEFAULT_TERMINAL_SCROLLBACK_LINES,
+  DEFAULT_UI_FONT_SIZE,
+  MAX_CODE_FONT_SIZE,
   MAX_TERMINAL_SCROLLBACK_LINES,
+  MAX_UI_FONT_SIZE,
+  MIN_CODE_FONT_SIZE,
   MIN_TERMINAL_SCROLLBACK_LINES,
+  MIN_UI_FONT_SIZE,
   loadAppSettingsFromStorage as loadAppSettingsFromStoragePure,
   loadSettingsFromStorage as loadSettingsFromStoragePure,
+  parseClampedFontSize,
   parseTerminalScrollbackLines,
+  sanitizeFontFamily,
   saveAppSettings as saveAppSettingsPure,
   type AppSettings,
   type DesktopSettingsBridge,
@@ -35,10 +43,18 @@ export {
   APP_SETTINGS_KEY,
   DEFAULT_APP_SETTINGS,
   DEFAULT_CLIENT_SETTINGS,
+  DEFAULT_CODE_FONT_SIZE,
   DEFAULT_TERMINAL_SCROLLBACK_LINES,
+  DEFAULT_UI_FONT_SIZE,
+  MAX_CODE_FONT_SIZE,
   MAX_TERMINAL_SCROLLBACK_LINES,
+  MAX_UI_FONT_SIZE,
+  MIN_CODE_FONT_SIZE,
   MIN_TERMINAL_SCROLLBACK_LINES,
+  MIN_UI_FONT_SIZE,
+  parseClampedFontSize,
   parseTerminalScrollbackLines,
+  sanitizeFontFamily,
 };
 export type {
   AppSettings,
@@ -136,6 +152,21 @@ export function useSettings(): UseSettingsReturn {
       if (updates.terminalScrollbackLines !== undefined) {
         appUpdates.terminalScrollbackLines = updates.terminalScrollbackLines;
       }
+      if (updates.uiFontFamily !== undefined) {
+        appUpdates.uiFontFamily = updates.uiFontFamily;
+      }
+      if (updates.monoFontFamily !== undefined) {
+        appUpdates.monoFontFamily = updates.monoFontFamily;
+      }
+      if (updates.uiFontSize !== undefined) {
+        appUpdates.uiFontSize = updates.uiFontSize;
+      }
+      if (updates.codeFontSize !== undefined) {
+        appUpdates.codeFontSize = updates.codeFontSize;
+      }
+      if (updates.syntaxTheme !== undefined) {
+        appUpdates.syntaxTheme = updates.syntaxTheme;
+      }
       const promises: Promise<void>[] = [];
       if (Object.keys(appUpdates).length > 0) {
         promises.push(appSettings.updateSettings(appUpdates));