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/stats.go

@@ -0,0 +1,24 @@
+package utils
+
+type ContainerStats struct {
+	ID          string
+	CPU         float64
+	Memory      uint64
+	MemoryLimit uint64
+	RX          uint64
+	TX          uint64
+}
+
+func ContainerStatsFromDocker(stats interface{}, id string) *ContainerStats {
+	var cpu float64
+	var mem, memLimit, rx, tx uint64
+
+	return &ContainerStats{
+		ID:          id,
+		CPU:         cpu,
+		Memory:      mem,
+		MemoryLimit: memLimit,
+		RX:          rx,
+		TX:          tx,
+	}
+}