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

internal/jsonutil/jsonutil.go

@@ -0,0 +1,131 @@
+// Package jsonutil provides shared helpers for working with untyped JSON
+// values (map[string]any) that come from API responses across all providers.
+package jsonutil
+
+import (
+	"strconv"
+	"strings"
+)
+
+// StringFromAny converts a dynamic JSON value to a string.
+// Numeric types are formatted without trailing zeroes.
+func StringFromAny(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 ""
+	}
+}
+
+// IntFromAny converts a dynamic JSON value to an int.
+// Handles int, int64, float64, and string types.
+func IntFromAny(v any) int {
+	switch t := v.(type) {
+	case int:
+		return t
+	case int32:
+		return int(t)
+	case int64:
+		return int(t)
+	case float64:
+		return int(t)
+	case string:
+		i, _ := strconv.Atoi(strings.TrimSpace(t))
+		return i
+	default:
+		return 0
+	}
+}
+
+// FloatFromAny converts a dynamic JSON value to a float64.
+func FloatFromAny(v any) float64 {
+	switch t := v.(type) {
+	case float64:
+		return t
+	case int:
+		return float64(t)
+	case int64:
+		return float64(t)
+	default:
+		return 0
+	}
+}
+
+// BoolFromAny converts a dynamic JSON value to a bool.
+// Supports bool, string ("true"/"1"/"yes"), and numeric types.
+func BoolFromAny(v any) bool {
+	switch t := v.(type) {
+	case bool:
+		return t
+	case string:
+		l := strings.ToLower(strings.TrimSpace(t))
+		return l == "1" || l == "true" || l == "yes"
+	case int:
+		return t != 0
+	case int64:
+		return t != 0
+	case float64:
+		return t != 0
+	default:
+		return false
+	}
+}
+
+// FirstNonEmpty returns the first string in items that is non-empty after trimming.
+func FirstNonEmpty(items ...string) string {
+	for _, item := range items {
+		if strings.TrimSpace(item) != "" {
+			return strings.TrimSpace(item)
+		}
+	}
+	return ""
+}
+
+// NestedMap returns the value at m[key] as a map[string]any.
+// Returns an empty map if the key is missing or the value is not a map.
+func NestedMap(m map[string]any, key string) map[string]any {
+	v, ok := m[key].(map[string]any)
+	if !ok {
+		return map[string]any{}
+	}
+	return v
+}
+
+// NestedAny traverses a chain of map keys and returns the final value.
+func NestedAny(v map[string]any, keys ...string) any {
+	cur := any(v)
+	for _, key := range keys {
+		m, ok := cur.(map[string]any)
+		if !ok {
+			return nil
+		}
+		cur = m[key]
+	}
+	return cur
+}
+
+// NestedString traverses a chain of map keys and returns the final value as a string.
+func NestedString(v map[string]any, keys ...string) string {
+	return StringFromAny(NestedAny(v, keys...))
+}
+
+// TitleCase capitalises the first rune of s. This is a simple ASCII replacement
+// for the deprecated strings.Title function, suitable for source names like
+// "qobuz" → "Qobuz".
+func TitleCase(s string) string {
+	if s == "" {
+		return s
+	}
+	r := []rune(s)
+	if r[0] >= 'a' && r[0] <= 'z' {
+		r[0] -= 'a' - 'A'
+	}
+	return string(r)
+}