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/sentry/sentry_test.go

@@ -0,0 +1,47 @@
+package sentry
+
+import "testing"
+
+func TestEnvironment(t *testing.T) {
+	tests := []struct {
+		version string
+		want    string
+	}{
+		{"", "development"},
+		{"dev", "development"},
+		{"0.1.0-dev", "development"},
+		{"1.0.0", "production"},
+		{"0.3.5", "production"},
+		{"2.0.0-beta", "production"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.version, func(t *testing.T) {
+			got := environment(tt.version)
+			if got != tt.want {
+				t.Errorf("environment(%q) = %q, want %q", tt.version, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestInitNoOp(t *testing.T) {
+	// With empty dsn (default in tests), Init should be a no-op
+	Init("1.0.0")
+	// Should not panic
+}
+
+func TestCloseNoOp(t *testing.T) {
+	// Close should be safe to call without Init
+	Close()
+}
+
+func TestCaptureErrorNil(t *testing.T) {
+	// Should not panic with nil error
+	CaptureError(nil, "test")
+}
+
+func TestSetUser(t *testing.T) {
+	// Should not panic without initialization
+	SetUser("agent-123")
+}