Port envd from e2b with internalized shared packages and Connect RPC

- Copy envd source from e2b-dev/infra, internalize shared dependencies
  into envd/internal/shared/ (keys, filesystem, id, smap, utils)
- Switch from gRPC to Connect RPC for all envd services
- Update module paths to git.omukk.dev/wrenn/{sandbox,sandbox/envd}
- Add proto specs (process, filesystem) with buf-based code generation
- Implement full envd: process exec, filesystem ops, port forwarding,
  cgroup management, MMDS integration, and HTTP API
- Update main module dependencies (firecracker SDK, pgx, goose, etc.)
- Remove placeholder .gitkeep files replaced by real implementations

envd/internal/shared/utils/ptr.go

@@ -0,0 +1,43 @@
+package utils
+
+import "fmt"
+
+func ToPtr[T any](v T) *T {
+	return &v
+}
+
+func FromPtr[T any](s *T) T {
+	if s == nil {
+		var zero T
+
+		return zero
+	}
+
+	return *s
+}
+
+func Sprintp[T any](s *T) string {
+	if s == nil {
+		return "<nil>"
+	}
+
+	return fmt.Sprintf("%v", *s)
+}
+
+func DerefOrDefault[T any](s *T, defaultValue T) T {
+	if s == nil {
+		return defaultValue
+	}
+
+	return *s
+}
+
+func CastPtr[S any, T any](s *S, castFunc func(S) T) *T {
+	if s == nil {
+		return nil
+	}
+
+	t := castFunc(*s)
+
+	return &t
+}