Add pre-update/clean backup feature

- Backup deletion paths before update to sd:/backup/OmniNX/{version}
- Backup deletion paths before clean install to sd:/backup/OmniNX/pre-omninx
- Best-effort backup: continue install even if some copies fail
- Fix directory creation: ensure parent dirs exist before folder_copy
- Step 1 for update: Backup; Step 1-2 for clean: user data + pre-omninx backup

Co-authored-by: Cursor <cursoragent@cursor.com>

source/backup.c

@@ -6,14 +6,97 @@
 #include "fs.h"
 #include <libs/fatfs/ff.h>
 #include <string.h>
+#include <stdarg.h>
 #include <utils/sprintf.h>
 
+#define BACKUP_PATH_MAX 270
+
 // Check if file/directory exists
 static bool path_exists(const char *path) {
     FILINFO fno;
     return (f_stat(path, &fno) == FR_OK);
 }
 
+// Create all parent directories for a path (mkdir -p style)
+static void ensure_parent_dirs(const char *full_path) {
+    char buf[BACKUP_PATH_MAX];
+    int n = (int)strlen(full_path);
+    if (n >= BACKUP_PATH_MAX) return;
+    memcpy(buf, full_path, n + 1);
+
+    for (int i = 4; i < n; i++) {
+        if (buf[i] == '/') {
+            buf[i] = '\0';
+            f_mkdir(buf);
+            buf[i] = '/';
+        }
+    }
+}
+
+// Copy a single path (file or dir) to backup base, preserving SD structure
+static int backup_single_path(const char *src_path, const char *backup_base) {
+    FILINFO fno;
+    if (f_stat(src_path, &fno) != FR_OK)
+        return FR_OK;
+
+    const char *relative = src_path;
+    if (strncmp(relative, "sd:/", 4) == 0)
+        relative += 4;
+
+    if (fno.fattrib & AM_DIR) {
+        const char *last_slash = strrchr(relative, '/');
+        char parent[BACKUP_PATH_MAX];
+        if (last_slash && last_slash > relative) {
+            s_printf(parent, "%s/%.*s", backup_base, (int)(last_slash - relative), relative);
+            /* Create full parent hierarchy (e.g. atmosphere, atmosphere/contents) */
+            ensure_parent_dirs(parent);
+            f_mkdir(parent);  /* Ensure parent exists; FR_EXIST is fine */
+            return folder_copy(src_path, parent);
+        } else {
+            ensure_parent_dirs(backup_base);
+            return folder_copy(src_path, backup_base);
+        }
+    } else {
+        char dst_path[BACKUP_PATH_MAX];
+        s_printf(dst_path, "%s/%s", backup_base, relative);
+        ensure_parent_dirs(dst_path);
+        return file_copy(src_path, dst_path);
+    }
+}
+
+// Backup all paths from varargs lists (same structure as delete_path_lists_grouped)
+int backup_deletion_lists(const char *backup_base, ...) {
+    va_list ap;
+    const char **list;
+    int res = FR_OK;
+
+    /* FatFS f_mkdir only creates the last component; parent must exist first */
+    ensure_parent_dirs(BACKUP_BASE_PATH);
+    res = f_mkdir(BACKUP_BASE_PATH);
+    if (res != FR_OK && res != FR_EXIST)
+        return res;
+
+    ensure_parent_dirs(backup_base);
+    res = f_mkdir(backup_base);
+    if (res != FR_OK && res != FR_EXIST)
+        return res;
+
+    va_start(ap, backup_base);
+    while ((list = va_arg(ap, const char **)) != NULL) {
+        for (int i = 0; list[i] != NULL; i++) {
+            if (path_exists(list[i])) {
+                int copy_res = backup_single_path(list[i], backup_base);
+                if (copy_res != FR_OK && res == FR_OK)
+                    res = copy_res;  // Remember first error but keep going
+            }
+        }
+    }
+    va_end(ap);
+
+    /* Best-effort: return FR_OK so install continues even if some copies failed */
+    return FR_OK;
+}
+
 // Backup user data before clean install
 int backup_user_data(void) {
     int res;