feat(ui): theme skins — OG Codeman, Daylight Green, Daylight Blue

Add a per-device skin switcher in App Settings → Display:
- Three skins via html[data-skin]: og (original Codeman look),
  daylight-green, and daylight-blue (new default). Per-skin CSS-variable
  token blocks; the v1.0 "Carbon Aurora" component polish is scoped to
  non-og skins and parameterized so green/blue differ only by token values.
- Self-hosted Manrope (UI) + JetBrains Mono (terminal) variable fonts,
  served from /fonts (no external CDN, CSP-safe via font-src 'self').
- Per-skin xterm terminal theme with live re-theming of open terminals on
  skin change; skin-aware --term-bg so the terminal background fills cleanly
  (fixes the variable-height gap above the toolbar).
- Pre-paint inline script applies the saved skin before first paint (no
  flash); persisted per-device in localStorage + the settings blob, and
  kept out of the server settings payload (device-local).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/public/app.js

@@ -580,6 +580,7 @@ class CodemanApp {
     const _kbSettings = this.loadAppSettingsFromStorage();
     if (_kbSettings.extendedKeyboardBar) KeyboardAccessoryBar.setMode('extended');
     this.applyHeaderVisibilitySettings();
+    this.applySkin();
     this.applyTabWrapSettings();
     this.applyMonitorVisibility();
     // Remove mobile-init class now that JS has applied visibility settings.
@@ -637,6 +638,7 @@ class CodemanApp {
     // Load server-stored settings (async, re-applies visibility after load)
     this.loadAppSettingsFromServer(settingsPromise).then(() => {
       this.applyHeaderVisibilitySettings();
+      this.applySkin();
       this.applyTabWrapSettings();
       this.applyMonitorVisibility();
     });