Refactor: comprehensive cleanup and modularization

- Extracted common JSON parsing helpers into internal/jsonutil
- Removed duplicated helper functions from provider packages
- Removed dead code in internal/app/app.go and downloader.go
- Replaced deprecated strings.Title with jsonutil.TitleCase
- Added graceful shutdown with signal handling in main.go
- Split monolithic cmd/rip/main.go into args.go, helpers.go, lastfm.go, search.go

cmd/rip/args.go

@@ -0,0 +1,211 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"streamrip-go/internal/config"
+)
+
+type smokeOptions struct {
+	qualitySet bool
+	quality    int
+	ignoreDB   bool
+}
+
+type globalOptions struct {
+	configPath  string
+	folder      string
+	noDB        bool
+	qualitySet  bool
+	quality     int
+	codecSet    bool
+	codec       string
+	noProgress  bool
+	noSSLVerify bool
+	verbose     bool
+	command     string
+	commandArgs []string
+}
+
+func parseGlobalArgs(args []string) (globalOptions, error) {
+	opts := globalOptions{}
+	for i := 0; i < len(args); i++ {
+		arg := args[i]
+		if arg == "" {
+			continue
+		}
+		if !strings.HasPrefix(arg, "-") {
+			opts.command = arg
+			if i+1 < len(args) {
+				opts.commandArgs = append([]string(nil), args[i+1:]...)
+			}
+			return opts, nil
+		}
+
+		switch {
+		case arg == "-ndb" || arg == "--no-db":
+			opts.noDB = true
+		case arg == "--no-progress":
+			opts.noProgress = true
+		case arg == "--no-ssl-verify":
+			opts.noSSLVerify = true
+		case arg == "-v" || arg == "--verbose":
+			opts.verbose = true
+		case arg == "-f" || arg == "--folder":
+			if i+1 >= len(args) {
+				return globalOptions{}, fmt.Errorf("%s requires a value", arg)
+			}
+			opts.folder = strings.TrimSpace(args[i+1])
+			i++
+		case strings.HasPrefix(arg, "--folder="):
+			opts.folder = strings.TrimSpace(strings.TrimPrefix(arg, "--folder="))
+		case arg == "--config-path":
+			if i+1 >= len(args) {
+				return globalOptions{}, fmt.Errorf("--config-path requires a value")
+			}
+			opts.configPath = strings.TrimSpace(args[i+1])
+			i++
+		case strings.HasPrefix(arg, "--config-path="):
+			opts.configPath = strings.TrimSpace(strings.TrimPrefix(arg, "--config-path="))
+		case arg == "-q" || arg == "--quality":
+			if i+1 >= len(args) {
+				return globalOptions{}, fmt.Errorf("%s requires a value", arg)
+			}
+			q, err := strconv.Atoi(args[i+1])
+			if err != nil || q < 0 || q > 4 {
+				return globalOptions{}, fmt.Errorf("invalid quality %q (expected 0-4)", args[i+1])
+			}
+			opts.qualitySet = true
+			opts.quality = q
+			i++
+		case strings.HasPrefix(arg, "--quality="):
+			qRaw := strings.TrimSpace(strings.TrimPrefix(arg, "--quality="))
+			q, err := strconv.Atoi(qRaw)
+			if err != nil || q < 0 || q > 4 {
+				return globalOptions{}, fmt.Errorf("invalid quality %q (expected 0-4)", qRaw)
+			}
+			opts.qualitySet = true
+			opts.quality = q
+		case arg == "-c" || arg == "--codec":
+			if i+1 >= len(args) {
+				return globalOptions{}, fmt.Errorf("%s requires a value", arg)
+			}
+			codec, err := normalizeCodec(args[i+1])
+			if err != nil {
+				return globalOptions{}, err
+			}
+			opts.codecSet = true
+			opts.codec = codec
+			i++
+		case strings.HasPrefix(arg, "--codec="):
+			codecRaw := strings.TrimSpace(strings.TrimPrefix(arg, "--codec="))
+			codec, err := normalizeCodec(codecRaw)
+			if err != nil {
+				return globalOptions{}, err
+			}
+			opts.codecSet = true
+			opts.codec = codec
+		default:
+			return globalOptions{}, fmt.Errorf("unknown global option %q", arg)
+		}
+	}
+	return opts, nil
+}
+
+func normalizeCodec(raw string) (string, error) {
+	codec := strings.ToUpper(strings.TrimSpace(raw))
+	switch codec {
+	case "ALAC", "FLAC", "MP3", "AAC", "VORBIS":
+		return codec, nil
+	case "OGG":
+		return "VORBIS", nil
+	default:
+		return "", fmt.Errorf("unsupported codec %q (expected ALAC, FLAC, OGG, MP3, AAC)", raw)
+	}
+}
+
+func applyGlobalConfigOverrides(cfg *config.Config, opts globalOptions) {
+	if opts.folder != "" {
+		cfg.Session.Downloads.Folder = opts.folder
+	}
+	if opts.noDB {
+		cfg.Session.Database.DownloadsEnabled = false
+	}
+	if opts.qualitySet {
+		cfg.Session.Qobuz.Quality = opts.quality
+		cfg.Session.Tidal.Quality = opts.quality
+		cfg.Session.Deezer.Quality = opts.quality
+		cfg.Session.Soundcloud.Quality = opts.quality
+	}
+	if opts.codecSet {
+		cfg.Session.Conversion.Enabled = true
+		cfg.Session.Conversion.Codec = opts.codec
+	}
+	if opts.noProgress {
+		cfg.Session.CLI.ProgressBars = false
+	}
+	if opts.noSSLVerify {
+		cfg.Session.Downloads.VerifySSL = false
+	}
+}
+
+func errorWithActionableHint(err error, opts globalOptions) string {
+	if err == nil {
+		return ""
+	}
+	msg := err.Error()
+	if opts.noSSLVerify {
+		return msg
+	}
+	lower := strings.ToLower(msg)
+	if strings.Contains(lower, "x509") || strings.Contains(lower, "certificate") || strings.Contains(lower, "tls") || strings.Contains(lower, "ssl") {
+		return msg + " (hint: try again with --no-ssl-verify)"
+	}
+	return msg
+}
+
+func parseSmokeOptions(args []string, minQuality int, maxQuality int) (smokeOptions, error) {
+	opts := smokeOptions{}
+	for _, arg := range args {
+		switch arg {
+		case "--force", "--ignore-db":
+			opts.ignoreDB = true
+		default:
+			q, err := parseQuality(arg, minQuality, maxQuality)
+			if err != nil {
+				return smokeOptions{}, fmt.Errorf("unknown option %q", arg)
+			}
+			opts.quality = q
+			opts.qualitySet = true
+		}
+	}
+	return opts, nil
+}
+
+func parseQuality(raw string, min int, max int) (int, error) {
+	q, err := strconv.Atoi(raw)
+	if err != nil {
+		return 0, err
+	}
+	if q < min || q > max {
+		return 0, fmt.Errorf("quality must be %d-%d, got %d", min, max, q)
+	}
+	return q, nil
+}
+
+func asString(v any) string {
+	switch t := v.(type) {
+	case string:
+		return t
+	case int:
+		return strconv.Itoa(t)
+	case int64:
+		return strconv.FormatInt(t, 10)
+	case float64:
+		return strconv.FormatFloat(t, 'f', -1, 64)
+	default:
+		return ""
+	}
+}