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/daemon_test.go

@@ -0,0 +1,55 @@
+package cmd
+
+import "testing"
+
+func TestDeriveWSURL(t *testing.T) {
+	tests := []struct {
+		apiURL  string
+		agentID string
+		want    string
+	}{
+		{"https://torrentclaw.com", "agent-123", "wss://unarr.torrentclaw.com/ws/agent-123"},
+		{"http://localhost:3000", "a1", ""},        // localhost skipped
+		{"http://127.0.0.1:3000", "a1", ""},        // 127.0.0.1 skipped
+		{"https://torrentclaw.com/", "a1", "wss://unarr.torrentclaw.com/ws/a1"},
+		{"https://api.example.io", "x", "wss://unarr.api.example.io/ws/x"},
+		{"", "agent-123", ""},
+		{"https://torrentclaw.com", "", ""},
+		{"", "", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.apiURL+"_"+tt.agentID, func(t *testing.T) {
+			got := deriveWSURL(tt.apiURL, tt.agentID)
+			if got != tt.want {
+				t.Errorf("deriveWSURL(%q, %q) = %q, want %q", tt.apiURL, tt.agentID, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestFormatSpeedLog(t *testing.T) {
+	tests := []struct {
+		bps  int64
+		want string
+	}{
+		{0, "0 B/s"},
+		{500, "500 B/s"},
+		{1023, "1023 B/s"},
+		{1024, "1 KB/s"},
+		{10240, "10 KB/s"},
+		{1048576, "1.0 MB/s"},
+		{5242880, "5.0 MB/s"},
+		{1073741824, "1.0 GB/s"},
+		{2147483648, "2.0 GB/s"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.want, func(t *testing.T) {
+			got := formatSpeedLog(tt.bps)
+			if got != tt.want {
+				t.Errorf("formatSpeedLog(%d) = %q, want %q", tt.bps, got, tt.want)
+			}
+		})
+	}
+}