fix: check-deps installs all required system packages via apt

scripts/check_deps.sh now checks and installs all prerequisites:
git, curl, openssl, python3, python3-cryptography, docker, docker-compose.
Runs apt-get update only once if anything needs installing.
Also adds current user to docker group if missing.
Makefile calls it with sudo so it has the rights to install packages.

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

Makefile

@@ -39,7 +39,7 @@ help:
 
 # Setup commands
 check-deps:
-	@sh scripts/check_deps.sh
+	@sudo sh scripts/check_deps.sh
 
 setup: check-deps
 	@echo "Setting up Personal Internet Cell..."