dashboard: show 'o' (open script) in the no-system help panel too

The empty-dashboard panel (early_help) is a separate hint list from the
loaded-system one, and didn't list the new o/s keys — so 'o' worked but wasn't
advertised when no system is loaded (exactly when you'd use it). Add 'o' to
early_help and mention it in the 'no system loaded' line. (s/x need a system,
so they stay out of the empty-state panel.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/tui/screen_dashboard.cpp

@@ -44,6 +44,7 @@ Component Tui::BuildDashboardScreen() {
 
       Element early_help = RenderHelpPanel("dashboard", {
           {"c",      "console"},
+          {"o",      "open/run a script"},
           {"a",      "analyze"},
           {"h",      "help screen"},
           {"q",      "quit"},
@@ -57,7 +58,7 @@ Component Tui::BuildDashboardScreen() {
               hbox({
                   vbox({
                       text("  no system loaded — run 'new' or 'restore <file>'") | dim,
-                      text("  (press 'c' for the console, or Ctrl-P for the palette)") | dim,
+                      text("  (press 'o' to open a script, 'c' for the console, Ctrl-P for the palette)") | dim,
                       filler(),
                   }) | flex,
                   separator(),