feat: initial commit — unarr CLI

Search, inspect, stream, and download torrents from the terminal.
Replaces the entire *arr stack with a single binary.

internal/engine/method.go

@@ -0,0 +1,58 @@
+package engine
+
+import "context"
+
+// DownloadMethod identifies a download strategy.
+type DownloadMethod string
+
+const (
+	MethodTorrent DownloadMethod = "torrent"
+	MethodDebrid  DownloadMethod = "debrid"
+	MethodUsenet  DownloadMethod = "usenet"
+)
+
+// Progress is emitted by downloaders during a download.
+type Progress struct {
+	DownloadedBytes int64
+	TotalBytes      int64
+	SpeedBps        int64 // bytes per second
+	ETA             int   // seconds remaining
+	Peers           int   // connected peers (torrent only)
+	Seeds           int   // connected seeds (torrent only)
+	FileName        string
+}
+
+// Result is returned when a download completes successfully.
+type Result struct {
+	FilePath string
+	FileName string
+	Method   DownloadMethod
+	Size     int64
+}
+
+// Downloader is the interface every download method must implement.
+type Downloader interface {
+	// Method returns which method this downloader implements.
+	Method() DownloadMethod
+
+	// Available reports whether this method can handle the given task.
+	// For torrent: always true if infoHash is set.
+	// For debrid: checks if cached on debrid service.
+	// For usenet: checks if NZB is available.
+	Available(ctx context.Context, task *Task) (bool, error)
+
+	// Download starts the download. It blocks until completion or error.
+	// Progress is reported via progressCh at regular intervals.
+	// outputDir is where files should be written.
+	Download(ctx context.Context, task *Task, outputDir string, progressCh chan<- Progress) (*Result, error)
+
+	// Pause suspends an in-progress download but keeps partial files on disk
+	// so the download can be resumed later.
+	Pause(taskID string) error
+
+	// Cancel aborts an in-progress download and removes partial files.
+	Cancel(taskID string) error
+
+	// Shutdown gracefully shuts down the downloader.
+	Shutdown(ctx context.Context) error
+}