feat: add migrate command, media server detection, and debrid auto-config

- Migration wizard from Sonarr/Radarr/Prowlarr (unarr migrate) [pre-beta]
  - Auto-detect instances via Docker, config files, port scan, Prowlarr
  - Import wanted list (monitored+missing movies/series)
  - Import download history and blocklist to avoid re-downloading
  - Extract debrid tokens from *arr download clients
  - Quality profile mapping to preferred_quality config
  - DISTINCT ON PostgreSQL query for optimal torrent selection
  - JSON export with --dry-run --json (text to stderr, JSON to stdout)
- Media server detection (Plex/Jellyfin/Emby) in unarr init
  - Detects library paths and offers them as download directory options
- Debrid auto-configuration in unarr init
  - Scans *arr instances for debrid tokens
  - Validates and saves via API if user confirms
- New preferred_quality setting in config (2160p/1080p/720p)
- Library scan command (unarr scan) with ffprobe metadata extraction

internal/library/mediainfo/lang_test.go

@@ -0,0 +1,64 @@
+package mediainfo
+
+import "testing"
+
+func TestNormalizeLang(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"", "und"},
+		{"eng", "en"},
+		{"spa", "es"},
+		{"fre", "fr"},
+		{"fra", "fr"},
+		{"ger", "de"},
+		{"deu", "de"},
+		{"en", "en"},
+		{"es", "es"},
+		{"English", "en"},
+		{"SPANISH", "es"},
+		{"Japanese", "ja"},
+		{"jpn", "ja"},
+		{"chi", "zh"},
+		{"zho", "zh"},
+		{"und", "und"},
+		{"xyz", "xyz"}, // unknown → lowercase passthrough
+		{"POR", "pt"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := NormalizeLang(tt.input)
+			if got != tt.want {
+				t.Errorf("NormalizeLang(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestComputeLanguages(t *testing.T) {
+	tracks := []AudioTrack{
+		{Lang: "en", Codec: "aac", Channels: 2},
+		{Lang: "es", Codec: "ac3", Channels: 6},
+		{Lang: "en", Codec: "dts", Channels: 6}, // duplicate
+		{Lang: "und", Codec: "aac", Channels: 2},
+		{Lang: "", Codec: "aac", Channels: 2},
+	}
+
+	langs := ComputeLanguages(tracks)
+
+	if len(langs) != 2 {
+		t.Fatalf("expected 2 languages, got %d: %v", len(langs), langs)
+	}
+	if langs[0] != "en" || langs[1] != "es" {
+		t.Errorf("expected [en es], got %v", langs)
+	}
+}
+
+func TestComputeLanguagesEmpty(t *testing.T) {
+	langs := ComputeLanguages(nil)
+	if len(langs) != 0 {
+		t.Errorf("expected empty, got %v", langs)
+	}
+}