feat(ui): add app launcher and NomadNet MVP

lib/tdeck_ui/UI/LXMF/NavigationStack.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <array>
+#include <cstddef>
+
+namespace UI::LXMF {
+
+enum class Route {
+    HOME,
+    MESSAGES,
+    CHAT,
+    COMPOSE,
+    NETWORK,
+    ANNOUNCES,
+    STATUS,
+    RADIO_ACTIVITY,
+    QR,
+    PROPAGATION_NODES,
+    NOMADNET,
+    SETTINGS,
+    CALL,
+};
+
+class NavigationStack {
+public:
+    static constexpr std::size_t MAX_DEPTH = 12;
+
+    Route current() const { return _current; }
+    std::size_t depth() const { return _depth; }
+
+    void navigate(Route route) {
+        if (route == _current) return;
+        if (_depth == MAX_DEPTH) {
+            // Preserve the root entry so a saturated stack still unwinds Home.
+            for (std::size_t i = 2; i < MAX_DEPTH; ++i) _stack[i - 1] = _stack[i];
+            --_depth;
+        }
+        _stack[_depth++] = _current;
+        _current = route;
+    }
+
+    bool back() {
+        if (_depth == 0) return false;
+        _current = _stack[--_depth];
+        return true;
+    }
+
+    void home() {
+        _depth = 0;
+        _current = Route::HOME;
+    }
+
+    // Replace is for restoring a route after a transient call without adding
+    // an artificial history entry.
+    void replace(Route route) { _current = route; }
+
+private:
+    Route _current = Route::HOME;
+    std::array<Route, MAX_DEPTH> _stack{};
+    std::size_t _depth = 0;
+};
+
+} // namespace UI::LXMF