Kiosk: System Name entry in System Settings

Adds a System Name text-entry page (hint 'e.g. Living Room', 1-40 char
validation) and a data-driven System Settings row for it. Saving persists
locally and nudges the background sync; conflict/invalid results surface
the message and restore the previous name. Extends the settings-menu
tests.

src/system_name_page.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include "page.h"
+#include "text_cache.h"
+#include <SDL3_ttf/SDL_ttf.h>
+#include <string>
+
+// Text-entry page for the Kiosk's System Name (a human-readable label for this
+// License Key). Saves locally first, then syncs in the background so the UI is
+// never blocked on the network.
+class SystemNamePage : public Page {
+public:
+    void onPush(AppState& state) override;
+    void onResume(AppState& state) override;
+    void onPause(AppState& state) override;
+    void onPop(AppState& state) override;
+    void handleEvent(const SDL_Event& event) override;
+    void update(float dt) override;
+    void render(SDL_Renderer* renderer) override;
+
+private:
+    void createFonts();
+    void destroyFonts();
+    void destroyTextures();
+    void submit();
+    void pollSyncResult();
+
+    AppState* state_ = nullptr;
+    std::string storedValue_;
+    std::string input_;
+    std::string statusMessage_;
+    bool statusIsError_ = false;
+
+    TTF_Font* fontTitle_ = nullptr;
+    TTF_Font* fontHeader_ = nullptr;
+    TTF_Font* fontBody_ = nullptr;
+    TTF_Font* fontSmall_ = nullptr;
+
+    CachedText titleText_;
+    CachedText storedText_;
+    CachedText valueText_;
+    CachedText statusText_;
+    CachedText hintText_;
+};