M0 step 7: Settings, About, Storage, first-boot setup

- lib/apps_model (host-tested): SettingsMenu (rows, readable values,
  choices, validation messages) and SetupWizard (names, Region
  confirmation, timezone; saves only when finished)
- AppManager: modal Apps that Home/Back can't leave (setup wizard)
- SettingsApp: all settings plus Storage (usage, erase SD behind a
  dialog) and About (version, node id, battery, memory, uptime) pages,
  replacing the temporary Diagnostics App
- SetupApp: first-boot wizard, opened modally until SetupDone
- Node id and default names derived from the MAC like Meshtastic
- Widget demo is now hidden (About, then w)
- lib_ldf_mode = deep+ so libraries see each other's headers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/core/src/app_manager.h

@@ -23,24 +23,32 @@ class AppManager {
     std::vector<const AppInfo*> visibleApps() const;
 
     void begin();
-    bool open(const char* id);
+    bool open(const char* id);  // refused while a modal App runs
     void home();
 
+    // A modal App (e.g. the first-boot wizard) can't be left with Home or Back: those keys go to it,
+    // and it ends itself with endModal(), which returns to the Launcher.
+    bool openModal(const char* id);
+    void endModal();
+
     void handleKey(const KeyEvent& event);
     void update(uint32_t nowMs) { foreground_->update(nowMs); }
 
     App& foreground() const { return *foreground_; }
+    const char* foregroundTitle() const;  // nullptr for the Launcher
 
     // True once after the screen needs redrawing (App switch, or the App asked for it).
     bool takeRedraw();
 
    private:
     void switchTo(App& app);
+    App* find(const char* id) const;
 
     App& launcher_;
     App* foreground_;
     std::vector<AppInfo> apps_;
     bool redraw_ = true;
+    bool modal_ = false;
 };
 
 }  // namespace roro