tui: global script progress + dashboard source/restore work

Opening a script from the dashboard did nothing visually: the tick driving the
line-by-line loader was only handled in the console case, and the Computing…
overlay was console-only. Move both to the global layer — ticks now process on
any screen (the dashboard updates live as the script loads) and the Computing…
box overlays whatever screen is active. Add an 'r' dashboard shortcut to
restore a snapshot via the file picker (open mode, like 'o'). Dashboard help
hints (loaded + empty state) updated.

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

src/tui/screen_dashboard.cpp

@@ -45,6 +45,7 @@ Component Tui::BuildDashboardScreen() {
       Element early_help = RenderHelpPanel("dashboard", {
           {"c",      "console"},
           {"o",      "open/run a script"},
+          {"r",      "restore a snapshot"},
           {"a",      "analyze"},
           {"h",      "help screen"},
           {"q",      "quit"},
@@ -57,8 +58,8 @@ Component Tui::BuildDashboardScreen() {
               separator(),
               hbox({
                   vbox({
-                      text("  no system loaded — run 'new' or 'restore <file>'") | dim,
-                      text("  (press 'o' to open a script, 'c' for the console, Ctrl-P for the palette)") | dim,
+                      text("  no system loaded") | dim,
+                      text("  (press 'o' open a script · 'r' restore a snapshot · 'c' console · Ctrl-P palette)") | dim,
                       filler(),
                   }) | flex,
                   separator(),
@@ -312,6 +313,7 @@ Component Tui::BuildDashboardScreen() {
           {"x",      "export"},
           {"o",      "open/run a script"},
           {"s",      "save system"},
+          {"r",      "restore a snapshot"},
           {"PgUp",   "scroll up"},
           {"PgDn",   "scroll down"},
           {"Home",   "scroll top"},

src/tui/screen_main.cpp

@@ -89,18 +89,8 @@ Component Tui::BuildMainScreen(ScreenInteractive &screen) {
             }) | flex,
         }) | border;
 
-        if (loading) {
-            int total = (int)loading_lines.size();
-            std::string progress = std::to_string(loading_executed) + " / "
-                                 + std::to_string(total) + " lines";
-            auto modal = vbox({
-                text(" Computing… ") | bold | center,
-                separator(),
-                text(loading_filename) | center,
-                text(progress) | center,
-            }) | borderDouble | size(WIDTH, GREATER_THAN, 40);
-            return dbox({base, modal | center});
-        }
+        // The "Computing…" overlay is rendered globally in Run(), so it shows
+        // on whatever screen is active while a script loads.
         return base;
     });
 }

src/tui/tui.cpp

@@ -5,6 +5,7 @@
 #include <ftxui/component/component.hpp>
 #include <ftxui/component/event.hpp>
 #include <ftxui/component/screen_interactive.hpp>
+#include <ftxui/dom/elements.hpp>
 
 using namespace ftxui;
 
@@ -58,7 +59,28 @@ void Tui::Run() {
     auto with_error   = with_confirm
                       | Modal(BuildErrorModal(), &error_open);
 
-    auto root = CatchEvent(with_error, [this](Event e) {
+    // Global "Computing…" overlay while a script loads — visible on any screen
+    // (not just the console), so opening a script from the dashboard shows
+    // progress instead of looking frozen.
+    auto with_loading = Renderer(with_error, [this, with_error] {
+        Element base = with_error->Render();
+        if (!loading) return base;
+        std::string progress = std::to_string(loading_executed) + " / "
+                             + std::to_string((int)loading_lines.size()) + " lines";
+        Element modal = vbox({
+                            text(" Computing… ") | bold | center,
+                            separator(),
+                            text(loading_filename) | center,
+                            text(progress) | center,
+                        }) | borderDouble | size(WIDTH, GREATER_THAN, 40);
+        return dbox({base, modal | center});
+    });
+
+    auto root = CatchEvent(with_loading, [this](Event e) {
+        // Source ticks drive the line-by-line loader; handle them on ANY screen
+        // so `source` works from the dashboard, not only the console.
+        if (e == Event::Special("\x02tick")) { ProcessNextSourceLine(); return true; }
+
         // Modals own their events while open. Error modal sits on top.
         if (error_open || confirm_open || palette_open
             || sigtype_dialog_open || file_dialog.open) return false;
@@ -119,6 +141,15 @@ void Tui::Run() {
                                    });
                 return true;
             }
+            if (e == Event::Character("r")) {   // restore a saved system
+                OpenFileDialog("Restore system — load a snapshot",
+                               "dashboard.restore", "", {},
+                               [this](const std::string &path) {
+                                   Dispatch("restore " + path);
+                               },
+                               /*confirm_overwrite=*/false);  // opening, not saving
+                return true;
+            }
             return false;
 
         case 3:  // explore
@@ -153,7 +184,6 @@ void Tui::Run() {
             return false;
 
         default:  // 0: main (console / log view)
-            if (e == Event::Special("\x02tick")) { ProcessNextSourceLine(); return true; }
             if (e == Event::Escape) {
                 if (!pending.empty()) { CancelPending(); return true; }
                 screen_idx = 4; return true;