Review: System Title Bar only where it applies, docs, title repaint

- Preferences hides System Title Bar on macOS and the web, where it did
  nothing (it fell through to the plain checkbox row), and lists it with
  the window options instead of under Language.
- The next-launch note reuses "Applies the next time VectorCraft starts."
  instead of a second wording in every catalog.
- A new window title asks for one more frame: AppKit lays the title bar
  out again for it, and the next frame centres the window buttons (#968).
- The menu bar drops the bold branch for the VectorCraft menu it no
  longer shows; theme is imported where the tests use it.
- Docs: Language is Preferences › User Interface › Language (VectorCraft
  › Language on macOS); the control protocol describes System Title Bar;
  ROADMAP Last updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/prefscmds.rs

@@ -278,11 +278,11 @@ pub const PREF_SPECS: &[PrefSpec] = &[
     p!("toolGroupLabels", "User Interface", "", "Show Tool Group Labels", bool),
     p!("openDocumentsAsTabs", "User Interface", "", "Open Documents As Tabs", bool),
     p!("largeTabs", "User Interface", "", "Large Tabs", bool),
+    p!("systemTitleBar", "User Interface", "", "System Title Bar", bool),
     p!("uiScaling", "User Interface", "UI Scaling", "Scale", num(0.75, 2.0, "×")),
     p!("scaleCursorWithUi", "User Interface", "UI Scaling", "Scale Cursor Proportional to UI", bool),
     // `auto` or a language code the shell registers (`zh-hant`); the shell shows it as a dropdown.
     p!("interfaceLanguage", "User Interface", "Language", "Language", text),
-    p!("systemTitleBar", "User Interface", "", "System Title Bar", bool),
     // Performance
     p!("gpuPerformance", "Performance", "GPU Performance", "GPU Performance", bool),
     p!("animatedZoom", "Performance", "GPU Performance", "Animated Zoom", bool),