Drop newlib printf: log via BDK s_vprintf, add debug.ini log switch

log_write was the only vsnprintf user and pulled in newlib's printf,
dtoa, malloc and soft-float code (~44 KB). The payload now fits the
RCM limit again (146800 -> 102801 bytes); the build fails if it grows
past it. debug.ini log=1 writes sd:/config/omninx/install.log.

source/fs.c

@@ -9,14 +9,15 @@
 #include <string.h>
 #include <utils/sprintf.h>
 #include <stdarg.h>
-#include <stdio.h>
 
 #define FS_BUFFER_SIZE 0x100000  // 1MB copy buffer
-#define LOG_BUFFER_SIZE 512
+#define LOG_BUFFER_SIZE 1024 // fits two 255-char paths plus text
+#define LOG_SYNC_EVERY  16
 
 // Log file handle
 static FIL log_file;
 static bool log_enabled = false;
+static u32 log_lines;
 static char log_buf[LOG_BUFFER_SIZE];
 
 // Initialize log file
@@ -24,6 +25,7 @@ void log_init(const char *path) {
     int res = f_open(&log_file, path, FA_WRITE | FA_CREATE_ALWAYS);
     if (res == FR_OK) {
         log_enabled = true;
+        log_lines = 0;
         log_write("=== OmniNX Installer Log ===\n\n");
     }
 }
@@ -44,15 +46,19 @@ void log_write(const char *fmt, ...) {
     va_list args;
     va_start(args, fmt);
 
-    // Format the message
-    vsnprintf(log_buf, LOG_BUFFER_SIZE, fmt, args);
+    // BDK formatter (no newlib printf). Callers keep paths <= 255 chars.
+    u32 len = s_vprintf(log_buf, fmt, args);
 
     va_end(args);
 
-    // Write to file
     UINT bw;
-    f_write(&log_file, log_buf, strlen(log_buf), &bw);
-    f_sync(&log_file);  // Flush to ensure data is written
+    f_write(&log_file, log_buf, len, &bw);
+    if (++log_lines % LOG_SYNC_EVERY == 0)
+        f_sync(&log_file);
+}
+
+bool log_is_enabled(void) {
+    return log_enabled;
 }
 
 // Convert FatFS error code to string