Fix unused BG_COLOR warning and make show_splash() private

Move BG_COLOR inline into #ifndef block to avoid unused variable
when HAS_SPLASH_IMAGE is defined. Make show_splash() private since
it's only called internally from init_hardware_only().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/tdeck_ui/Hardware/TDeck/Display.cpp

@@ -174,14 +174,9 @@ void Display::set_power(bool on) {
 }
 
 void Display::show_splash() {
-    // Background color: #1D1A1E -> RGB565 0x18C3
-    static const uint16_t BG_COLOR = 0x18C3;
-
-#ifdef HAS_SPLASH_IMAGE
-    // Full-screen splash has background baked in — skip redundant fill
-#else
-    // No splash image — fill with background color
-    fill_screen(BG_COLOR);
+#ifndef HAS_SPLASH_IMAGE
+    // No splash image — fill with background color (#1D1A1E -> RGB565 0x18C3)
+    fill_screen(0x18C3);
 #endif
 
 #ifdef HAS_SPLASH_IMAGE

lib/tdeck_ui/Hardware/TDeck/Display.h

@@ -68,13 +68,6 @@ public:
      */
     static void draw_rect(int16_t x, int16_t y, int16_t w, int16_t h, uint16_t color);
 
-    /**
-     * Show boot splash image (centered Pyxis logo)
-     * Called during init_registers() before backlight turns on.
-     * Falls back to black screen if SplashImage.h not generated.
-     */
-    static void show_splash();
-
     /**
      * LVGL flush callback - called by LVGL to update display
      * Do not call directly - used internally by LVGL
@@ -82,6 +75,8 @@ public:
     static void lvgl_flush_cb(lv_disp_drv_t* drv, const lv_area_t* area, lv_color_t* color_p);
 
 private:
+    // Show boot splash image, called from init_hardware_only()
+    static void show_splash();
     // SPI commands for ST7789V
     enum Command : uint8_t {
         NOP = 0x00,