Replace config file with folder-based mapping

Mappings between local playlist folders and Kreativ-Tonies are now
expressed purely through the filesystem instead of a YAML config:

  <root>/<household_id>/<freier_name> [id=<tonie_id>]/*.mp3

- internal/library: discovers tonie folders from this structure
  (Discover/Filter), and scaffolds it automatically from the
  TonieCloud account (Scaffold), leaving already-existing folders
  (matched by tonie id) untouched
- internal/syncer: decoupled from the removed config package via a
  plain Target{TonieID, Folder, Prune} struct
- cmd/toni-sync: new `init --root PATH` command to scaffold the
  library; `sync [FILTER] --root PATH` now discovers targets from the
  folder tree instead of a config file; removed the `config` command
  group entirely
- Unit tests for folder discovery, filtering, and scaffolding

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/syncer/syncer.go

@@ -9,7 +9,6 @@ import (
 	"sort"
 	"strings"
 
-	"github.com/arnef/toni-sync/internal/config"
 	"github.com/arnef/toni-sync/internal/tonieapi"
 )
 
@@ -21,6 +20,15 @@ type TonieClient interface {
 	SortChaptersOfTonie(tonie tonieapi.CreativeTonie, chapters []tonieapi.Chapter) error
 }
 
+// Target describes what to sync: a local folder and the Kreativ-Tonie it maps to.
+// Mappings come from the on-disk library folder structure (see internal/library),
+// not from a separate config file.
+type Target struct {
+	TonieID string
+	Folder  string
+	Prune   bool // remove chapters that no longer have a matching local file
+}
+
 const maxTitleLength = 100
 
 var audioExtensions = map[string]bool{
@@ -110,13 +118,13 @@ func (p *Plan) NeedsChanges() bool {
 }
 
 // BuildPlan fetches the current state of the tonie and computes the diff against the local folder.
-func BuildPlan(client TonieClient, m config.Mapping) (*Plan, error) {
-	tonie, err := client.GetCreativeTonie(m.TonieID)
+func BuildPlan(client TonieClient, target Target) (*Plan, error) {
+	tonie, err := client.GetCreativeTonie(target.TonieID)
 	if err != nil {
 		return nil, err
 	}
 
-	tracks, err := ListLocalTracks(m.Folder)
+	tracks, err := ListLocalTracks(target.Folder)
 	if err != nil {
 		return nil, err
 	}
@@ -142,7 +150,7 @@ func BuildPlan(client TonieClient, m config.Mapping) (*Plan, error) {
 
 	var toRemove []tonieapi.Chapter
 	finalOrder := append([]string{}, orderedTitles...)
-	if m.Prune {
+	if target.Prune {
 		for _, c := range tonie.Chapters {
 			if !localTitles[c.Title] {
 				toRemove = append(toRemove, c)
@@ -166,14 +174,14 @@ func BuildPlan(client TonieClient, m config.Mapping) (*Plan, error) {
 }
 
 // ApplyPlan uploads missing tracks, then reorders/prunes chapters to match the local folder.
-func ApplyPlan(client TonieClient, m config.Mapping, plan *Plan) error {
+func ApplyPlan(client TonieClient, target Target, plan *Plan) error {
 	for _, track := range plan.ToUpload {
 		if err := client.UploadFileToTonie(plan.Tonie, track.Path, track.Title); err != nil {
 			return fmt.Errorf("uploading %s: %w", track.Path, err)
 		}
 	}
 
-	refreshed, err := client.GetCreativeTonie(m.TonieID)
+	refreshed, err := client.GetCreativeTonie(target.TonieID)
 	if err != nil {
 		return fmt.Errorf("refetching tonie after upload: %w", err)
 	}