feat: bundled Nerd Font symbols fallback + per-device terminal font setting

Shell prompts using Nerd Font glyphs (powerline, p10k/starship folder and
git icons) rendered as missing-glyph boxes: the built-in xterm stack has no
private-use-area symbols, and phones have no Nerd Fonts installed at all.

- Bundle Symbols Nerd Font Mono (icons-only, MIT, 1.2MB woff2) served from
  fonts/ and appended to the terminal stack before monospace — browsers fall
  back per glyph, so icons render everywhere while text stays in the text
  fonts. font-display: block + preload keep tofu out of xterm's glyph atlas.
- New per-device terminalFontFamily setting (App Settings > Terminal &
  Input > Font): prepended to the built-in stack, never a replacement, so
  the symbols fallback and final monospace always survive. Applied live on
  save (refit + echo-overlay refreshFont, mirroring setFontSize).
- Single source for both xterm surfaces: TERMINAL_FONT_DEFAULT_STACK +
  resolveTerminalFontFamily() in constants.js, unit-tested.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VjnbbZRBuvR5E3SDouwXr9

src/web/public/panels-ui.js

@@ -2279,7 +2279,7 @@ Object.assign(CodemanApp.prototype, {
       const terminal = new Terminal({
         theme: { ...window.codemanCurrentXtermTheme() },
         minimumContrastRatio: window.codemanCurrentSkinIsLight() ? 4.5 : 1,
-        fontFamily: '"Fira Code", "Cascadia Code", "JetBrains Mono", "SF Mono", Monaco, monospace',
+        fontFamily: window.CodemanTerminalFont.resolve(this.loadAppSettingsFromStorage?.().terminalFontFamily),
         fontSize: 12,
         lineHeight: 1.2,
         cursorBlink: true,