Add jukebox_maker web app v1.0

Go web application for filling USB drives with media files.
Runs in Docker on Unraid with /media, /mnt/usb, /config volumes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/config/config.go

@@ -0,0 +1,89 @@
+package config
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+	"path/filepath"
+)
+
+type OverwriteMode string
+type FileSelectMode string
+
+const (
+	OverwriteSkip   OverwriteMode = "skip"
+	OverwriteDelete OverwriteMode = "delete"
+
+	SelectNew FileSelectMode = "new"
+	SelectAll FileSelectMode = "all"
+)
+
+type SourceFolder struct {
+	Path    string `json:"path"`
+	Enabled bool   `json:"enabled"`
+}
+
+type Config struct {
+	ReserveFreeGB  float64        `json:"reserve_free_gb"`
+	Sources        []SourceFolder `json:"sources"`
+	OverwriteMode  OverwriteMode  `json:"overwrite_mode"`
+	FileSelectMode FileSelectMode `json:"file_select_mode"`
+	AutoCopy       bool           `json:"auto_copy"`
+}
+
+func defaults() Config {
+	return Config{
+		ReserveFreeGB:  2.0,
+		OverwriteMode:  OverwriteSkip,
+		FileSelectMode: SelectNew,
+		AutoCopy:       false,
+	}
+}
+
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path)
+	if errors.Is(err, os.ErrNotExist) {
+		cfg := defaults()
+		return &cfg, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	cfg := defaults()
+	if err := json.Unmarshal(data, &cfg); err != nil {
+		return nil, err
+	}
+	return &cfg, nil
+}
+
+func Save(path string, cfg *Config) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return err
+	}
+	data, err := json.MarshalIndent(cfg, "", "  ")
+	if err != nil {
+		return err
+	}
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, data, 0o644); err != nil {
+		return err
+	}
+	return os.Rename(tmp, path)
+}
+
+func (c *Config) Validate() error {
+	if c.ReserveFreeGB < 0 {
+		return errors.New("reserve_free_gb must be >= 0")
+	}
+	switch c.OverwriteMode {
+	case OverwriteSkip, OverwriteDelete:
+	default:
+		return errors.New("overwrite_mode must be 'skip' or 'delete'")
+	}
+	switch c.FileSelectMode {
+	case SelectNew, SelectAll:
+	default:
+		return errors.New("file_select_mode must be 'new' or 'all'")
+	}
+	return nil
+}