refactor(config): rewrite config parser

This PR refactors the configuration parser, replacing the old parser implementation with a new, more structured approach that includes validation and improved organization.

Key changes:
- Complete rewrite of the configuration parser using a map-based structure with built-in validation
- Addition of comprehensive validator functions for configuration values
- Renamed numerous configuration getter methods for better consistency

internal/cli/cli.go

@@ -78,7 +78,7 @@ func Parse() {
 	flag.StringVar(&flagExportUserFeeds, "export-user-feeds", "", flagExportUserFeedsHelp)
 	flag.Parse()
 
-	cfg := config.NewParser()
+	cfg := config.NewConfigParser()
 
 	if flagConfigFile != "" {
 		config.Opts, err = cfg.ParseFile(flagConfigFile)