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/library/library_test.go

@@ -0,0 +1,91 @@
+package library
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func mkTonieDir(t *testing.T, householdPath, dirName string) string {
+	t.Helper()
+	p := filepath.Join(householdPath, dirName)
+	if err := os.MkdirAll(p, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	return p
+}
+
+func TestParseTonieDir(t *testing.T) {
+	name, id, ok := ParseTonieDir("Peppa Wutz [id=ef01-5678]")
+	if !ok || name != "Peppa Wutz" || id != "ef01-5678" {
+		t.Fatalf("unexpected parse result: name=%q id=%q ok=%v", name, id, ok)
+	}
+}
+
+func TestParseTonieDirNoMatch(t *testing.T) {
+	if _, _, ok := ParseTonieDir("just a folder"); ok {
+		t.Fatal("expected no match for folder without [id=...] suffix")
+	}
+}
+
+func TestDirName(t *testing.T) {
+	if got := DirName("Peppa/Wutz", "abc"); got != "Peppa-Wutz [id=abc]" {
+		t.Fatalf("unexpected dir name: %q", got)
+	}
+}
+
+func TestDiscover(t *testing.T) {
+	root := t.TempDir()
+	household := filepath.Join(root, "household-1")
+	if err := os.MkdirAll(household, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	mkTonieDir(t, household, "Peppa Wutz [id=tonie-1]")
+	mkTonieDir(t, household, "not-a-tonie-folder")
+
+	// A second household with one tonie.
+	household2 := filepath.Join(root, "household-2")
+	mkTonieDir(t, household2, "Gute Nacht [id=tonie-2]")
+
+	tonies, err := Discover(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(tonies) != 2 {
+		t.Fatalf("expected 2 tonies, got %d: %+v", len(tonies), tonies)
+	}
+
+	byID := map[string]Tonie{}
+	for _, tn := range tonies {
+		byID[tn.TonieID] = tn
+	}
+
+	got, ok := byID["tonie-1"]
+	if !ok || got.HouseholdID != "household-1" || got.Name != "Peppa Wutz" {
+		t.Fatalf("unexpected tonie-1 entry: %+v", got)
+	}
+	got2, ok := byID["tonie-2"]
+	if !ok || got2.HouseholdID != "household-2" || got2.Name != "Gute Nacht" {
+		t.Fatalf("unexpected tonie-2 entry: %+v", got2)
+	}
+}
+
+func TestFilter(t *testing.T) {
+	tonies := []Tonie{
+		{HouseholdID: "h1", TonieID: "t1", Name: "Peppa Wutz"},
+		{HouseholdID: "h2", TonieID: "t2", Name: "Gute Nacht"},
+	}
+
+	if got := Filter(tonies, ""); len(got) != 2 {
+		t.Fatalf("empty filter should return all, got %d", len(got))
+	}
+	if got := Filter(tonies, "peppa"); len(got) != 1 || got[0].TonieID != "t1" {
+		t.Fatalf("expected 1 match for 'peppa', got %+v", got)
+	}
+	if got := Filter(tonies, "h2"); len(got) != 1 || got[0].TonieID != "t2" {
+		t.Fatalf("expected 1 match for 'h2', got %+v", got)
+	}
+	if got := Filter(tonies, "nomatch"); len(got) != 0 {
+		t.Fatalf("expected no matches, got %+v", got)
+	}
+}