feat(maestro): navbar debug toggle for the HUD (#20)

Add an always-visible "debug" button to the topbar (next to the design-kit
shortcut) that toggles the debug HUD. Reflects the current state (lit in accent
when on) and stays in sync with the Ctrl+Shift+D keybind via the shared toggle
event.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/styles.css

@@ -1893,3 +1893,9 @@ textarea {
 .hud-v[data-activity="Idle"] {
   color: var(--muted);
 }
+
+/* debug-HUD navbar toggle: lit when the HUD is on. */
+.debug-toggle.is-active {
+  color: var(--accent);
+  border-color: var(--accent);
+}