chore: add setup script

[dargmuesli]

This pull request introduces major improvements to project documentation and developer onboarding, along with minor configuration and code adjustments. The most significant changes are the addition of comprehensive documentation files, a new automated setup script for local development, and updates to configuration files for improved usability and correctness.

Documentation and Onboarding Improvements:

• Added a detailed AGENTS.md file outlining project structure, documentation map, code style, git workflow, and deployment practices for contributors.
• Introduced a comprehensive CONTRIBUTING.md with step-by-step development setup instructions (both automated and manual), repository structure, and contribution guidelines.
• Added a SECURITY.md file describing the responsible disclosure policy for security vulnerabilities in Vibetype.
• Updated README.md to include CI badge, project overview, and clearer quickstart instructions, referencing the new documentation.

Developer Experience Enhancements:

• Added scripts/setup.sh, an interactive Bash script that automates local fullstack environment setup, including prerequisites check, repository cloning, and initial build/deploy steps.

Configuration and Code Adjustments:

• Changed dargstack.yaml to prompt for volume removal before deploying in development by setting remove: true.
• Removed explicit user: node:node from src/development/vibetype/compose.yaml and pruned the user in the production compose, likely to rely on image defaults or external configuration.
• Improved environment variable validation in src/development/zammad/configurations/docker-entrypoint.sh to require variable names to start with a letter or underscore, and simplified value assignment.

[Copilot]

Pull request overview

This PR improves developer onboarding for the stack repository by adding contributor/security documentation, introducing an interactive local setup script, and making a few small configuration adjustments to development/production Compose and dargstack behavior.

Changes:

• Added onboarding and policy documentation (AGENTS.md, CONTRIBUTING.md, SECURITY.md) and refreshed README.md quickstart guidance.
• Added scripts/setup.sh to automate cloning related repos and running dargstack build/deploy for local fullstack setup.
• Tweaked configuration: enable volume-removal prompting in dargstack.yaml, adjust compose user configuration, and tighten env var name validation in Zammad’s entrypoint.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
scripts/setup.sh	New interactive bootstrap script for cloning/building/deploying local dev stack.
CONTRIBUTING.md	New contributor guide describing setup modes and workflow guidelines.
README.md	New/updated project overview and quickstart pointing to the setup script and docs.
AGENTS.md	Added repository instructions (style, structure, dargstack workflow).
SECURITY.md	Added responsible disclosure policy.
dargstack.yaml	Enables prompting to remove volumes before deploy in development.
src/development/zammad/configurations/docker-entrypoint.sh	Tightened env var-name validation for env-file loading.
src/development/vibetype/compose.yaml	Removes explicit container user for vibetype dev service.
src/production/vibetype/compose.yaml	Removes the production override that pruned the user field.

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