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.h

@@ -76,7 +76,7 @@ int apply_configuration_from_event(const cJSON* event);
 int apply_runtime_config_handlers(const cJSON* old_event, const cJSON* new_event);
 
 // Utility functions
-char** find_existing_nrdb_files(void);
+char** find_existing_db_files(void);
 char* extract_pubkey_from_filename(const char* filename);
 
 #endif /* CONFIG_H */