Add cross-platform bash script equivalent of esignet-service/Makefile (Linux + Windows Git Bash)

[sacrana0]

Summary

Replace esignet-service/Makefile with a shell script that runs on both Linux and Windows (Git Bash). make is not available out-of-the-box on Windows, forcing contributors to install it separately or run commands manually. A portable bash script removes that dependency and gives a single entry point across platforms. The existing Makefile will be removed once the script reaches parity.

Goals

• Single bash script (e.g. esignet-service/make.sh) exposing the same targets as the Makefile: help, keys, build, run/dev, test, lint, lint-install, smoke, docker-build, docker-run, update-thunder, tidy, clean, distclean.
• Runs unmodified on Linux and Windows Git Bash.
• Loads .env and honors the same overridable variables (PORT, ISSUER_URL, DATA_DIR, SIGNING_KEY_PATH, AUTHN_PROVIDER, DOCKER_IMAGE, THUNDER_BRANCH, etc.).
• help output listing targets and effective environment, matching current behavior.
• Remove esignet-service/Makefile and update any references (README, CI, docs) to use make.sh.

Non-goals

• Supporting native Windows shells (cmd, PowerShell) — Git Bash only.
• Adding new build targets beyond what the Makefile already provides.

Acceptance criteria

• ./make.sh help lists all targets and current env values.
• ./make.sh keys|build|run|test|lint|smoke|tidy|clean|distclean behave equivalently to the matching make targets.
• ./make.sh docker-build and docker-run produce the same image/run behavior.
• ./make.sh update-thunder resolves and updates the thunder replace directive in go.mod.
• Verified working on Linux and Windows Git Bash.
• esignet-service/Makefile removed and all references updated to make.sh.