docs(contribs): add description field to all contribs YAML files

[httpdss]

Problem

The YAML files under structkit/contribs/ had no description field, making it impossible to quickly understand what each structure generates without reading its full content.

Solution

Added a top-level description: > field to every YAML file under structkit/contribs/, consistent with common StructKit conventions. Each description provides a concise, human-readable summary of what the structure creates or configures.

Changes

Added description to all 46 YAML files across:

• Root-level structures (ansible-playbook, chef-cookbook, ci-cd-pipelines, cloudformation-files, docker-files, documentation-template, git-hooks, helm-chart, kubernetes-manifests, vagrant-files)
• configs/ (chglog, codeowners, devcontainer, editor-config, eslint, jshint, kubectl, prettier)
• github/chatmodes/ (plan)
• github/instructions/ (generic)
• github/prompts/ (generic, react-form, security-api, struct)
• github/templates
• github/workflows/ (codeql, execute-tf-workflow, labeler, pre-commit, release-drafter, run-struct, stale)
• project/ (custom-structures, generic, go, java, n8n, nodejs, python, ruby, rust)
• prompts/ (run-struct-trigger)
• terraform/apps/ (aws-accounts, environments, generic, github-organization, init)
• terraform/modules/ (generic)

Testing

• All pre-commit hooks (check-yaml, end-of-file-fixer, trailing-whitespace) passed
• No existing structure content was modified, only descriptions were prepended