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/nntp/client_test.go

@@ -0,0 +1,131 @@
+package nntp
+
+import (
+	"bufio"
+	"bytes"
+	"testing"
+)
+
+func TestNewClient(t *testing.T) {
+	c := NewClient(Config{Host: "news.example.com", Port: 563, SSL: true})
+	if c.cfg.MaxConnections != 10 {
+		t.Errorf("default MaxConnections = %d, want 10", c.cfg.MaxConnections)
+	}
+	if c.cfg.Host != "news.example.com" {
+		t.Errorf("Host = %q", c.cfg.Host)
+	}
+}
+
+func TestNewClientCustomConnections(t *testing.T) {
+	c := NewClient(Config{Host: "news.example.com", Port: 563, MaxConnections: 20})
+	if c.cfg.MaxConnections != 20 {
+		t.Errorf("MaxConnections = %d, want 20", c.cfg.MaxConnections)
+	}
+}
+
+func TestNewClientZeroConnections(t *testing.T) {
+	c := NewClient(Config{Host: "news.example.com", Port: 563, MaxConnections: 0})
+	if c.cfg.MaxConnections != 10 {
+		t.Errorf("MaxConnections should default to 10, got %d", c.cfg.MaxConnections)
+	}
+}
+
+func TestNewClientNegativeConnections(t *testing.T) {
+	c := NewClient(Config{MaxConnections: -5})
+	if c.cfg.MaxConnections != 10 {
+		t.Errorf("MaxConnections should default to 10 for negative, got %d", c.cfg.MaxConnections)
+	}
+}
+
+func TestActiveConnections(t *testing.T) {
+	c := NewClient(Config{Host: "localhost", Port: 119})
+	if c.ActiveConnections() != 0 {
+		t.Errorf("ActiveConnections = %d, want 0", c.ActiveConnections())
+	}
+}
+
+func TestStatus(t *testing.T) {
+	c := NewClient(Config{Host: "news.example.com", Port: 563})
+	s := c.Status()
+	if s != "0 connections (0 pooled) to news.example.com:563" {
+		t.Errorf("Status = %q", s)
+	}
+}
+
+func TestCloseIdempotent(t *testing.T) {
+	c := NewClient(Config{Host: "localhost", Port: 119})
+	// Close should be idempotent
+	if err := c.Close(); err != nil {
+		t.Errorf("first Close: %v", err)
+	}
+	if err := c.Close(); err != nil {
+		t.Errorf("second Close: %v", err)
+	}
+}
+
+func TestArticleNotFoundError(t *testing.T) {
+	err := &ArticleNotFoundError{MessageID: "abc123@news.example.com"}
+	msg := err.Error()
+	if msg != "nntp: article not found: abc123@news.example.com" {
+		t.Errorf("Error() = %q", msg)
+	}
+}
+
+func TestReadDotBody(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{
+			"simple body",
+			"Hello World\r\n.\r\n",
+			"Hello World\n",
+		},
+		{
+			"multiline",
+			"Line 1\r\nLine 2\r\nLine 3\r\n.\r\n",
+			"Line 1\nLine 2\nLine 3\n",
+		},
+		{
+			"dot-stuffed line",
+			"..This starts with a dot\r\n.\r\n",
+			".This starts with a dot\n",
+		},
+		{
+			"empty body",
+			".\r\n",
+			"",
+		},
+		{
+			"binary-like data",
+			"=ybegin line=128 size=1024 name=test.bin\r\nsome encoded data\r\n=yend\r\n.\r\n",
+			"=ybegin line=128 size=1024 name=test.bin\nsome encoded data\n=yend\n",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := bufio.NewReader(bytes.NewBufferString(tt.input))
+			got, err := readDotBody(r)
+			if err != nil {
+				t.Fatalf("readDotBody: %v", err)
+			}
+			if string(got) != tt.want {
+				t.Errorf("readDotBody = %q, want %q", string(got), tt.want)
+			}
+		})
+	}
+}
+
+func TestReadDotBodyEOF(t *testing.T) {
+	// No dot terminator — should read until EOF
+	r := bufio.NewReader(bytes.NewBufferString("partial data\r\n"))
+	got, err := readDotBody(r)
+	if err != nil {
+		t.Fatalf("readDotBody EOF: %v", err)
+	}
+	if string(got) != "partial data\n" {
+		t.Errorf("readDotBody EOF = %q", string(got))
+	}
+}