feat(debug): theme x tab screenshot sweep + Debug options dialog

Add a debug tool that cycles every skin across every build-enabled tab and saves a
PNG of each to a timestamped folder under the config dir (screenshots/sweep_<ts>/)
— for gathering visual context on theme-specific UI work.

- App state machine (app_network.cpp): startScreenshotSweep() builds the
  skin+enabled-page lists, saves the current skin/page, and steps through them;
  updateScreenshotSweep() (top of App::render) pins the page + settles ~4 frames
  after each skin/page change (skin switches reload TOML + reset the acrylic
  capture, so they need to settle); wantsScreenshotThisFrame()/screenshotSweepPath()
  /onScreenshotCaptured() coordinate with main.cpp. Restores the original skin/page
  when done; nothing persisted.
- Framebuffer capture (main.cpp): read the finished frame and encode PNG via the
  bundled miniz (tdefl_write_image_to_png_file_in_memory_ex). GL reads FBO 0 (RGBA,
  bottom-up -> flip); DX11 copies the backbuffer to a staging texture + maps it
  (BGRA, top-down -> channel-swap). Alpha forced opaque.
- Settings UI: move the Verbose logging checkbox off the wallet row into a new
  "Debug options" button that opens a dialog housing the verbose toggle + a "Run
  screenshot sweep" button. New i18n keys.

Both platforms build; no-crash smoke verified.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -308,7 +308,16 @@ public:
     // UI navigation
     void setCurrentPage(ui::NavPage page);
     ui::NavPage getCurrentPage() const { return current_page_; }
-    
+
+    // Debug: screenshot sweep — cycles every skin x every enabled tab, one PNG each, into a
+    // timestamped folder under the config dir. Driven from App::render(); main.cpp polls
+    // wantsScreenshotThisFrame() after drawing the frame, saves screenshotSweepPath(), then calls
+    // onScreenshotCaptured() to advance. Transient — restores the original skin/page when done.
+    void startScreenshotSweep();
+    bool wantsScreenshotThisFrame() const { return sweep_capture_this_frame_; }
+    const std::string& screenshotSweepPath() const { return sweep_current_path_; }
+    void onScreenshotCaptured();
+
     // Dialog triggers (used by settings page to open modal dialogs)
     void showImportKeyDialog() { show_import_key_ = true; }
     void showExportKeyDialog() { show_export_key_ = true; }
@@ -638,6 +647,21 @@ private:
     ui::NavPage prev_page_    = ui::NavPage::Overview;
     float page_alpha_         = 1.0f;  // 0→1 fade on page switch
     bool  sidebar_collapsed_  = false; // true = icon-only mode
+
+    // Debug screenshot sweep state.
+    bool  screenshot_sweep_active_    = false;
+    bool  sweep_capture_this_frame_   = false;
+    int   sweep_skin_idx_             = 0;
+    int   sweep_page_idx_             = 0;
+    int   sweep_settle_frames_        = 0;   // frames to let a new skin/page settle before capturing
+    std::vector<std::string>  sweep_skins_;  // skin ids to cycle
+    std::vector<ui::NavPage>  sweep_pages_;  // enabled pages to cycle
+    std::string sweep_dir_;                  // output folder for this sweep
+    std::string sweep_current_path_;         // PNG path for the frame about to be captured
+    std::string sweep_saved_skin_;           // restore on completion
+    ui::NavPage sweep_saved_page_ = ui::NavPage::Overview;
+    void updateScreenshotSweep();            // called at the top of render() while active
+    void applySweepTarget();                 // apply current (skin,page), compute path, arm settle
     bool  sidebar_user_toggled_ = false; // user manually toggled — suppress auto-collapse
     float sidebar_width_anim_ = 0.0f;  // animated width (0 = uninitialized)
     float prev_dpi_scale_     = 0.0f;  // detect DPI changes to snap sidebar width