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/cmd/config_menu_test.go

@@ -0,0 +1,55 @@
+package cmd
+
+import "testing"
+
+func TestValidateSpeed(t *testing.T) {
+	tests := []struct {
+		input   string
+		wantErr bool
+	}{
+		{"", false},
+		{"0", false},
+		{" ", false},
+		{"10MB", false},
+		{"500KB", false},
+		{"1GB", false},
+		{"abc", true},
+		{"10XB", true},
+		{"-5MB", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			err := validateSpeed(tt.input)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateSpeed(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestValidateDuration(t *testing.T) {
+	tests := []struct {
+		input   string
+		wantErr bool
+	}{
+		{"", false},
+		{"30s", false},
+		{"1m", false},
+		{"5m", false},
+		{"1h", false},
+		{"2h30m", false},
+		{"abc", true},
+		{"30", true},
+		{"5x", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			err := validateDuration(tt.input)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateDuration(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
+			}
+		})
+	}
+}