Add streamdeck-ctl JSON control CLI

streamdeck-ctl reports device/daemon/key status as JSON and edits the
config (brightness, key set/clear/press, daemon control) so front-ends
don't have to reimplement YAML handling or device probing.

- internal/config/edit.go: comment-preserving, node-level YAML edits with
  atomic writes; key indices written as !!int so config.Load accepts them.
- internal/device: add model names, Lookup() and Present() for probing
  without opening the HID handle.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BjuZBBfzXqZgxRhxzJvkkC

internal/device/streamdeck.go

@@ -19,6 +19,7 @@ const VendorID = 0x0fd9
 
 // ModelInfo describes hardware-specific constants for a Stream Deck model.
 type ModelInfo struct {
+	Name        string
 	KeyCount    int
 	Cols        int
 	Rows        int
@@ -31,9 +32,35 @@ type ModelInfo struct {
 
 // models maps USB product IDs to their hardware specs.
 var models = map[uint16]ModelInfo{
-	0x00ba: {KeyCount: 32, Cols: 8, Rows: 4, ImageWidth: 96, ImageHeight: 96, FlipX: true, FlipY: true}, // XL v2
-	0x006c: {KeyCount: 32, Cols: 8, Rows: 4, ImageWidth: 96, ImageHeight: 96, FlipX: true, FlipY: true}, // XL v1
-	0x006d: {KeyCount: 15, Cols: 5, Rows: 3, ImageWidth: 72, ImageHeight: 72, FlipX: true, FlipY: true}, // MK.2
+	0x00ba: {Name: "Stream Deck XL v2", KeyCount: 32, Cols: 8, Rows: 4, ImageWidth: 96, ImageHeight: 96, FlipX: true, FlipY: true},
+	0x006c: {Name: "Stream Deck XL v1", KeyCount: 32, Cols: 8, Rows: 4, ImageWidth: 96, ImageHeight: 96, FlipX: true, FlipY: true},
+	0x006d: {Name: "Stream Deck MK.2", KeyCount: 15, Cols: 5, Rows: 3, ImageWidth: 72, ImageHeight: 72, FlipX: true, FlipY: true},
+}
+
+// Lookup returns the hardware spec for a product ID without opening the device.
+// Callers that only need geometry (key count, grid shape) can use this while the
+// daemon holds the HID handle.
+func Lookup(productID uint16) (ModelInfo, bool) {
+	m, ok := models[productID]
+	return m, ok
+}
+
+// Present reports whether a Stream Deck with the given USB IDs is currently
+// enumerated. It does not open the device, so it is safe to call while the
+// daemon has it open.
+func Present(vendorID, productID uint16) (bool, error) {
+	if err := hid.Init(); err != nil {
+		return false, fmt.Errorf("hid init: %w", err)
+	}
+	found := false
+	err := hid.Enumerate(vendorID, productID, func(*hid.DeviceInfo) error {
+		found = true
+		return nil
+	})
+	if err != nil {
+		return false, fmt.Errorf("hid enumerate: %w", err)
+	}
+	return found, nil
 }
 
 const (