Fix SD card integration and Lua game loading

- Fix SD card MISO pin (was using display MISO instead of SD MISO)
- Add FatFS mounting after SD card initialization
- Restore SPI baudrate on all SD init failure paths
- Add case-insensitive .lua file extension check
- Filter out hidden 8.3 filename entries
- Add SPI speed management functions for shared SPI bus
- Wrap all FatFS operations with SPI speed switching
- Restore display SPI speed (32 MHz) after SD operations
- Add debug output to Lua game loader

This fixes slow display refresh when SD card is present and enables
reliable Lua game loading from SD card /games directory.

lib/sd_card/sd_card.c

@@ -105,7 +105,7 @@ bool sd_card_init(const sd_card_config_t *config) {
     // Configure MISO pin for SPI (MUST be done for SD card reads to work)
     gpio_set_function(config->gpio_miso, GPIO_FUNC_SPI);
     
-    // Save current SPI speed
+    // Save current SPI speed to restore on failure
     uint baudrate = spi_get_baudrate(config->spi);
     
     // Slow down SPI for SD card initialization (100-400 kHz recommended)
@@ -128,6 +128,7 @@ bool sd_card_init(const sd_card_config_t *config) {
     
     if (r1 != SD_R1_IDLE_STATE) {
         printf("[SD] Card not responding to CMD0\n");
+        spi_set_baudrate(config->spi, baudrate);  // Restore original speed
         return false;  // Card not responding
     }
     
@@ -151,6 +152,7 @@ bool sd_card_init(const sd_card_config_t *config) {
         // Check if voltage range is supported
         if (ocr[2] != 0x01 || ocr[3] != 0xAA) {
             printf("[SD] Voltage range not supported\n");
+            spi_set_baudrate(config->spi, baudrate);  // Restore original speed
             return false;
         }
         
@@ -173,6 +175,7 @@ bool sd_card_init(const sd_card_config_t *config) {
         
         if (r1 != SD_R1_READY) {
             printf("[SD] ACMD41 initialization timeout\n");
+            spi_set_baudrate(config->spi, baudrate);  // Restore original speed
             return false;  // Initialization failed
         }
         
@@ -222,10 +225,12 @@ bool sd_card_init(const sd_card_config_t *config) {
             
             g_card_info.type = SD_CARD_TYPE_SD1;
         } else {
+            spi_set_baudrate(config->spi, baudrate);  // Restore original speed
             return false;  // Not supported
         }
         
         if (r1 != SD_R1_READY) {
+            spi_set_baudrate(config->spi, baudrate);  // Restore original speed
             return false;
         }
     }
@@ -237,6 +242,7 @@ bool sd_card_init(const sd_card_config_t *config) {
         sd_card_deselect();
         
         if (r1 != SD_R1_READY) {
+            spi_set_baudrate(config->spi, baudrate);  // Restore original speed
             return false;
         }
     }
@@ -392,14 +398,28 @@ bool sd_card_init_with_board_config(void) {
     static const sd_card_config_t config = {
         .spi = SD_SPI_PORT,
         .gpio_cs = SD_CS_PIN,
-        .gpio_miso = DISPLAY_MISO_PIN,
-        .gpio_mosi = DISPLAY_MOSI_PIN,
-        .gpio_sck = DISPLAY_SCK_PIN
+        .gpio_miso = SD_MISO_PIN,
+        .gpio_mosi = SD_MOSI_PIN,
+        .gpio_sck = SD_SCK_PIN
     };
     
     return sd_card_init(&config);
 }
 
+uint sd_card_set_spi_speed(void) {
+    if (!g_config) return 0;
+    
+    // Save current speed and set to SD card speed
+    uint current_speed = spi_get_baudrate(g_config->spi);
+    spi_set_baudrate(g_config->spi, 12500 * 1000);  // 12.5 MHz for SD card
+    return current_speed;
+}
+
+void sd_card_restore_spi_speed(uint baudrate) {
+    if (!g_config || baudrate == 0) return;
+    spi_set_baudrate(g_config->spi, baudrate);
+}
+
 bool sd_card_test_fatfs(void) {
     if (!g_card_info.initialized) {
         printf("SD Card not initialized\n");

lib/sd_card/sd_card.h

@@ -75,6 +75,19 @@ bool sd_card_init(const sd_card_config_t *config);
  */
 bool sd_card_init_with_board_config(void);
 
+/**
+ * Set SPI speed to SD card speed (12.5 MHz) before SD operations
+ * Call this before any FatFS file operations if SPI is shared with display
+ * @return Previous baudrate to restore later
+ */
+uint sd_card_set_spi_speed(void);
+
+/**
+ * Restore SPI speed after SD card operations
+ * @param baudrate Previous baudrate to restore
+ */
+void sd_card_restore_spi_speed(uint baudrate);
+
 /**
  * Get card information
  * @param info Pointer to info structure to fill