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/ratelimiter.go

@@ -0,0 +1,29 @@
+package utils
+
+import (
+	"time"
+)
+
+type RateLimiter struct {
+	lastTime    time.Time
+	minInterval time.Duration
+}
+
+func NewRateLimiter(interval time.Duration) *RateLimiter {
+	return &RateLimiter{
+		minInterval: interval,
+	}
+}
+
+func (r *RateLimiter) Allow() bool {
+	now := time.Now()
+	if now.Sub(r.lastTime) >= r.minInterval {
+		r.lastTime = now
+		return true
+	}
+	return false
+}
+
+func (r *RateLimiter) Reset() {
+	r.lastTime = time.Time{}
+}