Rewrite toni-sync in Go

- Replace the Python implementation with a Go module compiling to a
  single static binary (no Python/pip runtime dependency)
- internal/tonieapi: minimal, dependency-light HTTP client for the
  TonieCloud REST API (login, households, creative tonies, file
  upload via presigned S3 request, chapter add/sort/clear)
- internal/config: YAML-based mapping of local playlist folders to
  Kreativ-Tonies, credentials never stored
- internal/syncer: diff/apply logic (upload new tracks, prune removed
  chapters, reorder to match local file order), built against a
  TonieClient interface for testability
- cmd/toni-sync: Cobra CLI with `tonies list`, `config add/list/remove`,
  `sync [NAME|--all] [--dry-run]`
- Unit tests for config persistence and syncer plan/apply logic

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

internal/tonieapi/models.go

@@ -0,0 +1,49 @@
+package tonieapi
+
+// User is the currently logged in TonieCloud user.
+type User struct {
+	UUID  string `json:"uuid"`
+	Email string `json:"email"`
+}
+
+// Household is a TonieCloud household (a "family" account).
+type Household struct {
+	ID        string `json:"id"`
+	Name      string `json:"name"`
+	OwnerName string `json:"ownerName"`
+	Access    string `json:"access"`
+	CanLeave  bool   `json:"canLeave"`
+}
+
+// Chapter is a single audio chapter on a Creative Tonie.
+type Chapter struct {
+	ID          string  `json:"id"`
+	Title       string  `json:"title"`
+	File        string  `json:"file"`
+	Seconds     float64 `json:"seconds"`
+	Transcoding bool    `json:"transcoding"`
+}
+
+// CreativeTonie is a single Kreativ-Tonie figure.
+type CreativeTonie struct {
+	ID                string    `json:"id"`
+	HouseholdID       string    `json:"householdId"`
+	Name              string    `json:"name"`
+	ImageURL          string    `json:"imageUrl"`
+	SecondsRemaining  float64   `json:"secondsRemaining"`
+	SecondsPresent    float64   `json:"secondsPresent"`
+	ChaptersRemaining int       `json:"chaptersRemaining"`
+	ChaptersPresent   int       `json:"chaptersPresent"`
+	Transcoding       bool      `json:"transcoding"`
+	LastUpdate        *string   `json:"lastUpdate"`
+	Chapters          []Chapter `json:"chapters"`
+}
+
+// uploadRequest describes the pre-signed S3 upload target returned by POST /file.
+type uploadRequest struct {
+	Request struct {
+		URL    string            `json:"url"`
+		Fields map[string]string `json:"fields"`
+	} `json:"request"`
+	FileID string `json:"fileId"`
+}