Replace comments with stderr echo messages in post-create.sh

Co-authored-by: KSXGitHub <11488886+KSXGitHub@users.noreply.github.com>

Author: Copilot

.devcontainer/post-create.sh

@@ -1,12 +1,12 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Install Python dependencies
+echo "Installing Python dependencies..." >&2
 pip install toml
 
-# Install pnpm and project Node dependencies
+echo "Installing pnpm and project Node dependencies..." >&2
 npm install -g pnpm
 (cd ci/github-actions && pnpm install)
 
-# Install hyperfine via Cargo
+echo "Installing hyperfine via Cargo..." >&2
 cargo install hyperfine