fix(detect): wire up ports package for OpenBSD detection

The ports package was fully implemented but detect_openbsd.go still
returned nil candidates with a stale TODO. Wire up ports.New() so
OpenBSD systems can auto-detect their package manager.

Also adds:
- Unit tests for GetCapabilities with mock managers (base + full)
- Unit tests for Locker mutual exclusion
- Edge case tests for ports parser (empty input, whitespace, fallback)
- Minor dep updates (charmbracelet/ultraviolet, charmbracelet/x)

mutex_test.go

@@ -0,0 +1,45 @@
+package snack_test
+
+import (
+	"sync"
+	"sync/atomic"
+	"testing"
+
+	"github.com/gogrlx/snack"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLocker_MutualExclusion(t *testing.T) {
+	var l snack.Locker
+	var counter int64
+	var wg sync.WaitGroup
+	const goroutines = 50
+
+	wg.Add(goroutines)
+	for range goroutines {
+		go func() {
+			defer wg.Done()
+			l.Lock()
+			defer l.Unlock()
+			// If the lock works, only one goroutine touches
+			// the counter at a time.
+			cur := atomic.LoadInt64(&counter)
+			atomic.StoreInt64(&counter, cur+1)
+		}()
+	}
+	wg.Wait()
+	assert.Equal(t, int64(goroutines), atomic.LoadInt64(&counter))
+}
+
+func TestLocker_LockUnlock(t *testing.T) {
+	var l snack.Locker
+	var n int
+	// Should not deadlock; verifies lock/unlock cycle works twice.
+	l.Lock()
+	n++
+	l.Unlock()
+	l.Lock()
+	n++
+	l.Unlock()
+	assert.Equal(t, 2, n)
+}