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/library/scanner_test.go

@@ -0,0 +1,93 @@
+package library
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestDiscoverFiles(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create video files (need to be >= 100MB to pass size check)
+	largeContent := make([]byte, 101*1024*1024)
+
+	videoFiles := []string{"movie.mkv", "show.mp4", "clip.avi"}
+	for _, name := range videoFiles {
+		path := filepath.Join(dir, name)
+		if err := os.WriteFile(path, largeContent, 0o644); err != nil {
+			t.Fatalf("write %s: %v", name, err)
+		}
+	}
+
+	// Non-video files (should be excluded)
+	nonVideo := []string{"readme.txt", "cover.jpg", "subs.srt"}
+	for _, name := range nonVideo {
+		if err := os.WriteFile(filepath.Join(dir, name), largeContent, 0o644); err != nil {
+			t.Fatalf("write %s: %v", name, err)
+		}
+	}
+
+	// Small video file (should be excluded, < 100MB)
+	if err := os.WriteFile(filepath.Join(dir, "small.mkv"), []byte("small"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Excluded pattern (sample)
+	sampleDir := filepath.Join(dir, "sample")
+	os.MkdirAll(sampleDir, 0o755)
+	if err := os.WriteFile(filepath.Join(sampleDir, "sample.mkv"), largeContent, 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	files, err := discoverFiles(dir)
+	if err != nil {
+		t.Fatalf("discoverFiles: %v", err)
+	}
+
+	if len(files) != 3 {
+		t.Errorf("expected 3 files, got %d: %v", len(files), files)
+	}
+
+	// Check that all returned files are video extensions
+	for _, f := range files {
+		ext := filepath.Ext(f)
+		if ext != ".mkv" && ext != ".mp4" && ext != ".avi" {
+			t.Errorf("unexpected extension: %s", ext)
+		}
+	}
+}
+
+func TestDiscoverFilesEmptyDir(t *testing.T) {
+	dir := t.TempDir()
+
+	files, err := discoverFiles(dir)
+	if err != nil {
+		t.Fatalf("discoverFiles: %v", err)
+	}
+	if len(files) != 0 {
+		t.Errorf("expected 0 files, got %d", len(files))
+	}
+}
+
+func TestDiscoverFilesExcludePatterns(t *testing.T) {
+	dir := t.TempDir()
+	largeContent := make([]byte, 101*1024*1024)
+
+	excludeDirs := []string{"trailer", "featurette", "extras", "bonus"}
+	for _, name := range excludeDirs {
+		sub := filepath.Join(dir, name)
+		os.MkdirAll(sub, 0o755)
+		if err := os.WriteFile(filepath.Join(sub, "video.mkv"), largeContent, 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	files, err := discoverFiles(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(files) != 0 {
+		t.Errorf("expected 0 files (all excluded), got %d: %v", len(files), files)
+	}
+}