refactor: move internal/ to pkg/ for external importability

Moves all packages from internal/ to pkg/ so they can be imported
by external modules (needed for claude-pm integration).

- internal/app/ → pkg/app/
- internal/docker/ → pkg/docker/
- internal/config/ → pkg/config/
- internal/utils/ → pkg/utils/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/utils/scroll.go

@@ -0,0 +1,31 @@
+package utils
+
+type ScrollDirection int
+
+const (
+	ScrollUp ScrollDirection = iota
+	ScrollDown
+	ScrollPageUp
+	ScrollPageDown
+	ScrollHome
+	ScrollEnd
+)
+
+func (sd ScrollDirection) String() string {
+	switch sd {
+	case ScrollUp:
+		return "up"
+	case ScrollDown:
+		return "down"
+	case ScrollPageUp:
+		return "pageup"
+	case ScrollPageDown:
+		return "pagedown"
+	case ScrollHome:
+		return "home"
+	case ScrollEnd:
+		return "end"
+	default:
+		return "unknown"
+	}
+}