feat(seeding): wire seed ratio/time lifecycle into the torrent daemon

SeedRatio/SeedTime were declared on TorrentConfig but never consumed, and
SeedEnabled was hardcoded false in both constructors — the daemon never
seeded, and if forced it seeded forever.

- config: [downloads] seed_enabled/seed_ratio/seed_time (opt-in, off by default)
- daemon: parse seed_time + wire all three; startup log per target shape
- engine: seedTargetReached() (pure) + seedAndDrop() background monitor on a
  downloader-scoped seedCtx (not the task ctx, which dies when Download returns);
  drops the torrent on ratio (uploaded/size) OR time, whichever first; no target
  = seed until shutdown. Configurable check interval (tests lower it).
- fix: cleanup() now always drops — previously leaked the handle on error paths
  when seeding was enabled.
- refactor: dropTracked() helper shared by cleanup + post-seeding drop.

Tests: TestSeedTargetReached (9 cases) + ctx/no-target branches + loopback
swarm smoke (-tags smoke). Roadmap hueco closed.

internal/cmd/daemon.go

@@ -204,6 +204,9 @@ func runDaemonStart() error {
 	metaTimeout, _ := time.ParseDuration(cfg.Download.MetadataTimeout)
 	stallTimeout, _ := time.ParseDuration(cfg.Download.StallTimeout)
 
+	// Parse the seeding time target (0/"" = no time target — ratio-only or forever)
+	seedTime, _ := time.ParseDuration(cfg.Download.SeedTime)
+
 	// Create progress reporter — only used for stream tasks (handleStreamTask)
 	// The sync goroutine handles all regular progress reporting.
 	statusInterval, _ := time.ParseDuration(cfg.Daemon.StatusInterval)
@@ -273,7 +276,9 @@ func runDaemonStart() error {
 		MaxDownloadRate:    maxDl,
 		MaxUploadRate:      maxUl,
 		ListenPort:         cfg.Download.ListenPort,
-		SeedEnabled:        false,
+		SeedEnabled:        cfg.Download.SeedEnabled,
+		SeedRatio:          cfg.Download.SeedRatio,
+		SeedTime:           seedTime,
 		VPNTunnel:          vpnTunnel,
 	})
 	if err != nil {
@@ -291,6 +296,19 @@ func runDaemonStart() error {
 		log.Printf("Speed limits: download=%s upload=%s", dlStr, ulStr)
 	}
 
+	if cfg.Download.SeedEnabled {
+		switch {
+		case cfg.Download.SeedRatio > 0 && seedTime > 0:
+			log.Printf("[torrent] seeding enabled (stop at ratio %.2f or %s, whichever first)", cfg.Download.SeedRatio, seedTime)
+		case cfg.Download.SeedRatio > 0:
+			log.Printf("[torrent] seeding enabled (stop at ratio %.2f)", cfg.Download.SeedRatio)
+		case seedTime > 0:
+			log.Printf("[torrent] seeding enabled (stop after %s)", seedTime)
+		default:
+			log.Printf("[torrent] seeding enabled (no ratio/time target — seeds until shutdown)")
+		}
+	}
+
 	// Create debrid downloader
 	debridDl := engine.NewDebridDownloader()
 	usenetDl := engine.NewUsenetDownloader(agentClient)

internal/cmd/download.go

@@ -113,7 +113,9 @@ func runDownloadWithDeps(input, method string, deps downloadDeps) error {
 		MetadataTimeout: 15 * time.Minute,
 		StallTimeout:    10 * time.Minute,
 		MaxTimeout:      0, // unlimited
-		SeedEnabled:     false,
+		// One-shot foreground download: leech then exit. Seeding only makes sense
+		// for the always-on daemon (see DownloadConfig.SeedEnabled).
+		SeedEnabled: false,
 	})
 	if err != nil {
 		return fmt.Errorf("create downloader: %w", err)