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/mediaserver/detect_test.go

@@ -0,0 +1,98 @@
+package mediaserver
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestParsePlexSections(t *testing.T) {
+	body := `{
+		"MediaContainer": {
+			"Directory": [
+				{
+					"title": "Movies",
+					"Location": [{"path": "/data/media/movies"}]
+				},
+				{
+					"title": "TV Shows",
+					"Location": [{"path": "/data/media/tv"}]
+				}
+			]
+		}
+	}`
+
+	paths := parsePlexSections([]byte(body))
+	if len(paths) != 2 {
+		t.Fatalf("parsePlexSections = %d paths, want 2", len(paths))
+	}
+	if paths[0] != "/data/media/movies" {
+		t.Errorf("paths[0] = %q, want /data/media/movies", paths[0])
+	}
+	if paths[1] != "/data/media/tv" {
+		t.Errorf("paths[1] = %q, want /data/media/tv", paths[1])
+	}
+}
+
+func TestParsePlexSections_Empty(t *testing.T) {
+	paths := parsePlexSections([]byte(`{}`))
+	if len(paths) != 0 {
+		t.Errorf("parsePlexSections empty = %d paths, want 0", len(paths))
+	}
+}
+
+func TestParsePlexSections_InvalidJSON(t *testing.T) {
+	paths := parsePlexSections([]byte(`not json`))
+	if paths != nil {
+		t.Errorf("parsePlexSections invalid = %v, want nil", paths)
+	}
+}
+
+func TestJellyfinParsing(t *testing.T) {
+	body := `[
+		{"Locations": ["/media/movies"]},
+		{"Locations": ["/media/tv", "/media/anime"]}
+	]`
+
+	var folders []struct {
+		Locations []string `json:"Locations"`
+	}
+	if err := json.Unmarshal([]byte(body), &folders); err != nil {
+		t.Fatal(err)
+	}
+
+	var paths []string
+	for _, f := range folders {
+		paths = append(paths, f.Locations...)
+	}
+	if len(paths) != 3 {
+		t.Fatalf("got %d paths, want 3", len(paths))
+	}
+}
+
+func TestParentDir(t *testing.T) {
+	tests := []struct {
+		name   string
+		paths  []string
+		expect string
+	}{
+		{"empty", nil, ""},
+		{"single", []string{"/data/media/movies"}, "/data/media"},
+		{"siblings", []string{"/data/media/movies", "/data/media/tv"}, "/data/media"},
+		{"different roots", []string{"/data/movies", "/srv/tv"}, "/"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ParentDir(tt.paths)
+			// "/" is filtered out (returns "")
+			if tt.expect == "/" {
+				if got != "" {
+					t.Errorf("ParentDir = %q, want empty (root filtered)", got)
+				}
+				return
+			}
+			if got != tt.expect {
+				t.Errorf("ParentDir = %q, want %q", got, tt.expect)
+			}
+		})
+	}
+}