Fix emulator build script, UI rendering, and clean up repo

lib/serial_uploader.cpp

@@ -173,7 +173,7 @@ bool SerialUploader::complete_launch() {
     return launched;
 }
 
-bool SerialUploader::process() {
+bool SerialUploader::process(bool spi_busy) {
     if (state == IDLE) {
         // Check for "UPLOAD" command
         int c = getchar_timeout_us(0);
@@ -311,6 +311,9 @@ bool SerialUploader::process() {
     }
 
     if (state == WRITING_FILE) {
+        // Wait if SPI bus is busy (e.g. display refresh in progress on other core)
+        if (spi_busy) return false;
+
         if (write_file_to_sd()) {
             state = LAUNCHING_GAME;
             // Prepare for launch by scanning games, but don't actually launch yet

lib/serial_uploader.h

@@ -12,7 +12,8 @@ public:
 
     // Process incoming serial data (call this frequently in main loop)
     // Returns true if a game was launched
-    bool process();
+    // spi_busy: set to true if SPI bus is currently in use by another core (e.g. display refresh)
+    bool process(bool spi_busy = false);
 
     // Check if uploader wants to launch a game (after upload complete)
     bool wants_to_launch_game() const { return state == LAUNCHING_GAME; }