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.

games/lua_game.cpp

@@ -5,6 +5,7 @@
 
 #include "lua_game.h"
 #include "lua_bindings.h"
+#include "sd_card.h"
 #include <stdio.h>
 #include <string.h>
 
@@ -54,9 +55,13 @@ bool LuaGame::load_script() {
     FIL fil;
     FRESULT fr;
     
+    // Set SPI speed for SD card operations
+    uint prev_speed = sd_card_set_spi_speed();
+    
     // Open Lua script from SD card
     fr = f_open(&fil, script_path.c_str(), FA_READ);
     if (fr != FR_OK) {
+        sd_card_restore_spi_speed(prev_speed);
         error_message = "Failed to open file (FatFS error: ";
         error_message += std::to_string((int)fr);
         error_message += ")";
@@ -67,6 +72,7 @@ bool LuaGame::load_script() {
     FSIZE_t file_size = f_size(&fil);
     if (file_size == 0 || file_size > 64 * 1024) {  // Limit to 64KB
         f_close(&fil);
+        sd_card_restore_spi_speed(prev_speed);
         error_message = "Script file size invalid (0 or > 64KB)";
         return false;
     }
@@ -75,6 +81,7 @@ bool LuaGame::load_script() {
     char* script_buffer = new char[file_size + 1];
     if (!script_buffer) {
         f_close(&fil);
+        sd_card_restore_spi_speed(prev_speed);
         error_message = "Failed to allocate memory for script";
         return false;
     }
@@ -84,6 +91,9 @@ bool LuaGame::load_script() {
     fr = f_read(&fil, script_buffer, file_size, &bytes_read);
     f_close(&fil);
     
+    // Restore SPI speed immediately after file operations
+    sd_card_restore_spi_speed(prev_speed);
+    
     if (fr != FR_OK || bytes_read != file_size) {
         delete[] script_buffer;
         error_message = "Failed to read script file";