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/storage.ts

@@ -1,3 +1,4 @@
+import { isSyntaxThemeId, type SyntaxThemeId } from "@getpaseo/highlight";
 import type { QueryClient } from "@tanstack/react-query";
 import type { DesktopSettings } from "@/desktop/settings/desktop-settings";
 import { THEME_TO_UNISTYLES, type ThemeName } from "@/styles/theme";
@@ -15,12 +16,24 @@ const VALID_SERVICE_URL_BEHAVIORS = new Set<ServiceUrlBehavior>(["ask", "in-app"
 export const DEFAULT_TERMINAL_SCROLLBACK_LINES = 10_000;
 export const MIN_TERMINAL_SCROLLBACK_LINES = 0;
 export const MAX_TERMINAL_SCROLLBACK_LINES = 1_000_000;
+export const DEFAULT_UI_FONT_SIZE = 16; // == FONT_SIZE.base
+export const MIN_UI_FONT_SIZE = 11;
+export const MAX_UI_FONT_SIZE = 24;
+export const DEFAULT_CODE_FONT_SIZE = 12; // == FONT_SIZE.code
+export const MIN_CODE_FONT_SIZE = 9;
+export const MAX_CODE_FONT_SIZE = 22; // line-height 1.5×22=33 stays safe
+export const MAX_FONT_FAMILY_LENGTH = 200;
 
 export interface AppSettings {
   theme: ThemeName | "auto";
   sendBehavior: SendBehavior;
   serviceUrlBehavior: ServiceUrlBehavior;
   terminalScrollbackLines: number;
+  uiFontFamily: string; // "" = platform default UI stack
+  monoFontFamily: string; // "" = platform default mono stack
+  uiFontSize: number; // clamped px, default 16
+  codeFontSize: number; // clamped px, default 12
+  syntaxTheme: SyntaxThemeId; // default "auto"
 }
 
 export interface Settings extends AppSettings {
@@ -33,6 +46,11 @@ export const DEFAULT_CLIENT_SETTINGS: AppSettings = {
   sendBehavior: "interrupt",
   serviceUrlBehavior: "ask",
   terminalScrollbackLines: DEFAULT_TERMINAL_SCROLLBACK_LINES,
+  uiFontFamily: "",
+  monoFontFamily: "",
+  uiFontSize: DEFAULT_UI_FONT_SIZE,
+  codeFontSize: DEFAULT_CODE_FONT_SIZE,
+  syntaxTheme: "github",
 };
 
 export const DEFAULT_APP_SETTINGS: Settings = {
@@ -144,6 +162,31 @@ function pickAppSettings(stored: Partial<AppSettings>): Partial<AppSettings> {
   if (terminalScrollbackLines !== null) {
     result.terminalScrollbackLines = terminalScrollbackLines;
   }
+  const uiFontFamily = sanitizeFontFamily(stored.uiFontFamily);
+  if (uiFontFamily !== null) {
+    result.uiFontFamily = uiFontFamily;
+  }
+  const monoFontFamily = sanitizeFontFamily(stored.monoFontFamily);
+  if (monoFontFamily !== null) {
+    result.monoFontFamily = monoFontFamily;
+  }
+  const uiFontSize = parseClampedFontSize(stored.uiFontSize, {
+    min: MIN_UI_FONT_SIZE,
+    max: MAX_UI_FONT_SIZE,
+  });
+  if (uiFontSize !== null) {
+    result.uiFontSize = uiFontSize;
+  }
+  const codeFontSize = parseClampedFontSize(stored.codeFontSize, {
+    min: MIN_CODE_FONT_SIZE,
+    max: MAX_CODE_FONT_SIZE,
+  });
+  if (codeFontSize !== null) {
+    result.codeFontSize = codeFontSize;
+  }
+  if (typeof stored.syntaxTheme === "string" && isSyntaxThemeId(stored.syntaxTheme)) {
+    result.syntaxTheme = stored.syntaxTheme;
+  }
   return result;
 }
 
@@ -171,6 +214,42 @@ export function parseTerminalScrollbackLines(value: unknown): number | null {
   );
 }
 
+export function parseClampedFontSize(
+  value: unknown,
+  bounds: { min: number; max: number },
+): number | null {
+  let numericValue = NaN;
+  if (typeof value === "number") {
+    numericValue = value;
+  } else if (typeof value === "string" && value.trim().length > 0) {
+    numericValue = Number(value);
+  }
+  if (!Number.isFinite(numericValue)) {
+    return null;
+  }
+  return Math.min(bounds.max, Math.max(bounds.min, Math.floor(numericValue)));
+}
+
+export function sanitizeFontFamily(value: unknown): string | null {
+  if (typeof value !== "string") {
+    return null;
+  }
+  const trimmed = value.trim();
+  if (trimmed.length === 0) {
+    return ""; // explicit empty = default
+  }
+  if (trimmed.length > MAX_FONT_FAMILY_LENGTH) {
+    return null;
+  }
+  if (/[;{}<>]/.test(trimmed)) {
+    return null; // would break the web CSS font-family declaration
+  }
+  if ([...trimmed].some((char) => char.charCodeAt(0) <= 0x1f)) {
+    return null; // control chars would corrupt the font-family string
+  }
+  return trimmed; // quotes/commas are legit in stacks
+}
+
 async function loadLegacyDesktopSettingsFromStorage(storage: KeyValueStorage): Promise<{
   manageBuiltInDaemon?: boolean;
   releaseChannel?: ReleaseChannel;