v0.3.3 - Fix function naming consistency: rename find_existing_nrdb_files to find_existing_db_files

- Update function declaration in config.h
- Update function definition in config.c
- Update function calls in config.c and main.c
- Maintain consistency with .db file extension naming convention

This resolves the inconsistency between database file extension (.db) and function names (nrdb)

src/config.c

@@ -33,7 +33,7 @@ static cJSON* g_pending_config_event = NULL;
 // UTILITY FUNCTIONS
 // ================================
 
-char** find_existing_nrdb_files(void) {
+char** find_existing_db_files(void) {
     DIR *dir;
     struct dirent *entry;
     char **files = NULL;
@@ -342,7 +342,7 @@ int get_config_bool(const char* key, int default_value) {
 // ================================
 
 int is_first_time_startup(void) {
-    char** existing_files = find_existing_nrdb_files();
+    char** existing_files = find_existing_db_files();
     if (existing_files) {
         // Free the array
         for (int i = 0; existing_files[i]; i++) {