feat: silent pre-indexing with configurable status bar indicator

Port PR #979's silent pre-indexing and add an Indexing Display setting
(Popup / Status Bar Text / Status Bar Icon) so users can choose how
indexing feedback is shown.

Silent pre-indexing runs on text-only penultimate pages when a status
bar option is selected, with a standard requestUpdate to clear the
indicator. Image pages skip silent indexing to avoid e-ink grayscale
pipeline conflicts; the normal popup handles those transitions. Direct
chapter jumps always show the original small popup regardless of setting.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/CrossPointSettings.h

@@ -52,6 +52,13 @@ class CrossPointSettings {
     STATUS_BAR_MODE_COUNT
   };
 
+  enum INDEXING_DISPLAY {
+    INDEXING_POPUP = 0,
+    INDEXING_STATUS_TEXT = 1,
+    INDEXING_STATUS_ICON = 2,
+    INDEXING_DISPLAY_COUNT
+  };
+
   enum ORIENTATION {
     PORTRAIT = 0,       // 480x800 logical coordinates (current default)
     LANDSCAPE_CW = 1,   // 800x480 logical coordinates, rotated 180° (swap top/bottom)
@@ -157,6 +164,8 @@ class CrossPointSettings {
   uint8_t sleepScreenLetterboxFill = LETTERBOX_DITHERED;
   // Status bar settings
   uint8_t statusBar = FULL;
+  // Indexing feedback display mode (popup, status bar text, status bar icon)
+  uint8_t indexingDisplay = INDEXING_POPUP;
   // Text rendering settings
   uint8_t extraParagraphSpacing = 1;
   uint8_t textAntiAliasing = 1;