refactor: rewrite project from Rust to Go

- Replace Axum with Chi router
- Replace sqlx with pgx for PostgreSQL
- Replace tonic/prost with grpc-go
- Replace tracing with zerolog
- Update flake.nix for Go build with protoc generation
- Preserve all existing endpoints and functionality

Stack: Chi, pgx, grpc-go, zerolog, yaml.v3

internal/torrent/client.go

@@ -0,0 +1,49 @@
+package torrent
+
+import (
+	"context"
+	"errors"
+)
+
+var (
+	ErrNotConnected     = errors.New("not connected")
+	ErrAuthFailed       = errors.New("authentication failed")
+	ErrTorrentNotFound  = errors.New("torrent not found")
+	ErrInvalidRequest   = errors.New("invalid request")
+	ErrConnectionFailed = errors.New("connection failed")
+)
+
+type TorrentState string
+
+const (
+	StateDownloading TorrentState = "downloading"
+	StateSeeding     TorrentState = "seeding"
+	StatePaused      TorrentState = "paused"
+	StateQueued      TorrentState = "queued"
+	StateChecking    TorrentState = "checking"
+	StateError       TorrentState = "error"
+	StateUnknown     TorrentState = "unknown"
+)
+
+type TorrentInfo struct {
+	Hash          string       `json:"hash"`
+	Name          string       `json:"name"`
+	Size          uint64       `json:"size"`
+	Progress      float64      `json:"progress"`
+	DownloadSpeed uint64       `json:"download_speed"`
+	UploadSpeed   uint64       `json:"upload_speed"`
+	State         TorrentState `json:"state"`
+	SavePath      string       `json:"save_path"`
+}
+
+type Client interface {
+	Connect(ctx context.Context) error
+	Disconnect(ctx context.Context) error
+	ListTorrents(ctx context.Context) ([]TorrentInfo, error)
+	GetTorrent(ctx context.Context, hash string) (*TorrentInfo, error)
+	AddTorrentURL(ctx context.Context, url string, savePath *string) error
+	AddTorrentFile(ctx context.Context, data []byte, savePath *string) error
+	RemoveTorrent(ctx context.Context, hash string, deleteFiles bool) error
+	PauseTorrent(ctx context.Context, hash string) error
+	ResumeTorrent(ctx context.Context, hash string) error
+}