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/config/config.go

@@ -43,14 +43,20 @@ type DownloadConfig struct {
 	PreferredMethod  string `toml:"preferred_method"`
 	PreferredQuality string `toml:"preferred_quality"` // "2160p", "1080p", "720p" — hint for auto-selection
 	MaxConcurrent    int    `toml:"max_concurrent"`
-	MinFreeDiskMB    int    `toml:"min_free_disk_mb"` // refuse a download if it would leave less than this free (reserve to keep the FS healthy); default 2048, 0 = disable
+	MinFreeDiskMB    int    `toml:"min_free_disk_mb"`   // refuse a download if it would leave less than this free (reserve to keep the FS healthy); default 2048, 0 = disable
 	MaxDownloadSpeed string `toml:"max_download_speed"` // e.g. "10MB", "500KB", "0" = unlimited
 	MaxUploadSpeed   string `toml:"max_upload_speed"`   // e.g. "1MB", "0" = unlimited
-	MetadataTimeout  string `toml:"metadata_timeout"`   // e.g. "1h", "30m", "0" = unlimited (default: "0")
-	StallTimeout     string `toml:"stall_timeout"`      // e.g. "30m", "1h", "0" = unlimited (default: "30m")
-	ListenPort       int    `toml:"listen_port"`        // fixed port for incoming peer connections (default: 42069, 0 = random)
-	StreamPort       int    `toml:"stream_port"`        // fixed port for streaming HTTP server (default: 11818)
-	EnableUPnP       bool   `toml:"enable_upnp"`        // map StreamPort to the WAN via UPnP/NAT-PMP (default: false; opt-in)
+	// Seeding lifecycle (BitTorrent only). Off by default — the daemon leeches
+	// then drops the torrent. Enable to keep uploading after a download finishes;
+	// seeding stops at whichever target is hit first, or never if both are unset.
+	SeedEnabled     bool    `toml:"seed_enabled"`     // keep uploading after completion (default: false)
+	SeedRatio       float64 `toml:"seed_ratio"`       // stop once uploaded/size reaches this ratio (0 = no ratio target)
+	SeedTime        string  `toml:"seed_time"`        // stop after this long since completion, e.g. "24h" (0/"" = no time target)
+	MetadataTimeout string  `toml:"metadata_timeout"` // e.g. "1h", "30m", "0" = unlimited (default: "0")
+	StallTimeout    string  `toml:"stall_timeout"`    // e.g. "30m", "1h", "0" = unlimited (default: "30m")
+	ListenPort      int     `toml:"listen_port"`      // fixed port for incoming peer connections (default: 42069, 0 = random)
+	StreamPort      int     `toml:"stream_port"`      // fixed port for streaming HTTP server (default: 11818)
+	EnableUPnP      bool    `toml:"enable_upnp"`      // map StreamPort to the WAN via UPnP/NAT-PMP (default: false; opt-in)
 	// RequireStreamToken gates remote (non-loopback) /stream + /hls requests on a
 	// signed, short-lived token embedded in the URLs the agent reports. Default
 	// true (secure by default); loopback callers (local mpv/vlc) are always exempt.

internal/config/config_test.go

@@ -246,6 +246,55 @@ enabled = false
 	}
 }
 
+func TestLoadSeedingDefaultsOff(t *testing.T) {
+	tmp := t.TempDir()
+	path := filepath.Join(tmp, "config.toml")
+
+	// No [downloads] seeding keys — seeding must stay off by default.
+	os.WriteFile(path, []byte(`[auth]
+api_key = "tc_x"
+`), 0o644)
+
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatalf("Load failed: %v", err)
+	}
+	if cfg.Download.SeedEnabled {
+		t.Error("SeedEnabled should default to false")
+	}
+	if cfg.Download.SeedRatio != 0 {
+		t.Errorf("SeedRatio = %v, want 0", cfg.Download.SeedRatio)
+	}
+	if cfg.Download.SeedTime != "" {
+		t.Errorf("SeedTime = %q, want empty", cfg.Download.SeedTime)
+	}
+}
+
+func TestLoadSeedingExplicit(t *testing.T) {
+	tmp := t.TempDir()
+	path := filepath.Join(tmp, "config.toml")
+
+	os.WriteFile(path, []byte(`[downloads]
+seed_enabled = true
+seed_ratio = 2.0
+seed_time = "24h"
+`), 0o644)
+
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatalf("Load failed: %v", err)
+	}
+	if !cfg.Download.SeedEnabled {
+		t.Error("SeedEnabled = false, want true")
+	}
+	if cfg.Download.SeedRatio != 2.0 {
+		t.Errorf("SeedRatio = %v, want 2.0", cfg.Download.SeedRatio)
+	}
+	if cfg.Download.SeedTime != "24h" {
+		t.Errorf("SeedTime = %q, want 24h", cfg.Download.SeedTime)
+	}
+}
+
 func TestLoadInvalidTOML(t *testing.T) {
 	tmp := t.TempDir()
 	path := filepath.Join(tmp, "config.toml")