feat(cli): upgrade command, rich status, and version cache

- Replace `upgrade` stub with real command (alias for `self-update`)
- Also register `update` as alias: `unarr update` works too
- Rewrite `status` to show full config, disk usage, daemon state, and
  update availability with colored sections
- Add version check cache (1h TTL) so `status` is instant on repeat runs
- Guard against division by zero on empty filesystems
- Guard against negative durations from clock skew
- Guard against stale PID via heartbeat recency check (2 min)
- Add comprehensive test coverage across agent, engine, upgrade, usenet,
  arr, library, mediaserver, and UI packages
- Improve Makefile coverage target to exclude cmd/ glue code
- Fix stream handler resource cleanup and ffprobe error handling

internal/usenet/postprocess/pipeline_test.go

@@ -0,0 +1,156 @@
+package postprocess
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFindPar2File(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create par2 files of different sizes
+	mainPar2 := filepath.Join(dir, "content.par2")
+	vol1 := filepath.Join(dir, "content.vol000+01.par2")
+	vol2 := filepath.Join(dir, "content.vol001+02.par2")
+
+	os.WriteFile(mainPar2, make([]byte, 100), 0o644)   // smallest
+	os.WriteFile(vol1, make([]byte, 10000), 0o644)
+	os.WriteFile(vol2, make([]byte, 50000), 0o644)
+
+	files := map[string]string{
+		"content.par2":            mainPar2,
+		"content.vol000+01.par2": vol1,
+		"content.vol001+02.par2": vol2,
+	}
+
+	result := findPar2File(files)
+	if result != mainPar2 {
+		t.Errorf("findPar2File() = %q, want %q (smallest par2)", result, mainPar2)
+	}
+}
+
+func TestFindPar2FileNone(t *testing.T) {
+	files := map[string]string{
+		"video.mkv": "/tmp/video.mkv",
+		"subs.srt":  "/tmp/subs.srt",
+	}
+
+	result := findPar2File(files)
+	if result != "" {
+		t.Errorf("findPar2File() = %q, want empty", result)
+	}
+}
+
+func TestFindPar2FileEmpty(t *testing.T) {
+	result := findPar2File(map[string]string{})
+	if result != "" {
+		t.Errorf("findPar2File() = %q, want empty", result)
+	}
+}
+
+func TestFindFirstRarPart01(t *testing.T) {
+	files := map[string]string{
+		"movie.part01.rar": "/tmp/movie.part01.rar",
+		"movie.part02.rar": "/tmp/movie.part02.rar",
+		"movie.part03.rar": "/tmp/movie.part03.rar",
+	}
+
+	result := findFirstRar(files)
+	if result != "/tmp/movie.part01.rar" {
+		t.Errorf("findFirstRar() = %q, want part01.rar", result)
+	}
+}
+
+func TestFindFirstRarSingle(t *testing.T) {
+	files := map[string]string{
+		"movie.rar": "/tmp/movie.rar",
+		"movie.r00": "/tmp/movie.r00",
+		"movie.r01": "/tmp/movie.r01",
+	}
+
+	result := findFirstRar(files)
+	if result != "/tmp/movie.rar" {
+		t.Errorf("findFirstRar() = %q, want movie.rar (shortest)", result)
+	}
+}
+
+func TestFindFirstRarSplitFormat(t *testing.T) {
+	files := map[string]string{
+		"movie.001": "/tmp/movie.001",
+		"movie.002": "/tmp/movie.002",
+	}
+
+	result := findFirstRar(files)
+	if result != "/tmp/movie.001" {
+		t.Errorf("findFirstRar() = %q, want movie.001", result)
+	}
+}
+
+func TestFindFirstRarNone(t *testing.T) {
+	files := map[string]string{
+		"video.mkv": "/tmp/video.mkv",
+		"subs.srt":  "/tmp/subs.srt",
+	}
+
+	result := findFirstRar(files)
+	if result != "" {
+		t.Errorf("findFirstRar() = %q, want empty", result)
+	}
+}
+
+func TestFindMainFile(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create video files of different sizes
+	small := filepath.Join(dir, "small.mkv")
+	large := filepath.Join(dir, "large.mkv")
+	nonVideo := filepath.Join(dir, "readme.txt")
+
+	os.WriteFile(small, make([]byte, 1000), 0o644)
+	os.WriteFile(large, make([]byte, 5000), 0o644)
+	os.WriteFile(nonVideo, make([]byte, 9000), 0o644)
+
+	result := findMainFile(dir, []string{small, large, nonVideo})
+	if result != large {
+		t.Errorf("findMainFile() = %q, want %q (largest video)", result, large)
+	}
+}
+
+func TestFindMainFileFallbackToDir(t *testing.T) {
+	dir := t.TempDir()
+
+	video := filepath.Join(dir, "movie.mp4")
+	os.WriteFile(video, make([]byte, 5000), 0o644)
+
+	// Pass empty file list — should fallback to scanning dir
+	result := findMainFile(dir, nil)
+	if result != video {
+		t.Errorf("findMainFile() = %q, want %q (dir scan fallback)", result, video)
+	}
+}
+
+func TestFindMainFileEmpty(t *testing.T) {
+	dir := t.TempDir()
+	result := findMainFile(dir, nil)
+	if result != "" {
+		t.Errorf("findMainFile() = %q, want empty", result)
+	}
+}
+
+func TestFindMainFileMultipleFormats(t *testing.T) {
+	dir := t.TempDir()
+
+	mkv := filepath.Join(dir, "movie.mkv")
+	mp4 := filepath.Join(dir, "movie.mp4")
+	avi := filepath.Join(dir, "movie.avi")
+
+	os.WriteFile(mkv, make([]byte, 3000), 0o644)
+	os.WriteFile(mp4, make([]byte, 5000), 0o644) // largest
+	os.WriteFile(avi, make([]byte, 2000), 0o644)
+
+	result := findMainFile(dir, []string{mkv, mp4, avi})
+	if result != mp4 {
+		t.Errorf("findMainFile() = %q, want %q", result, mp4)
+	}
+}