Automate PR comments with Docker image link after base image push

[Copilot]

This PR implements automated PR commenting functionality that provides direct links to Docker images built for pull requests. When a PR modifies base image files (Dockerfile, package.json, etc.), the CI system now automatically creates or updates a comment with the Docker image details.

Changes Made

Workflow Enhancement

Added a new comment_docker_image job to .github/workflows/on_pr_test.yaml that:

• Runs after successful base image build when changes are detected
• Creates or updates PR comments idempotently (no duplicates)
• Uses minimal required permissions (pull-requests: write)
• Only executes for actual pull request events

Comment Features

The automated comment includes:

• Direct link to the Docker image: ghcr.io/orionrobots/orionrobots-site.base:${PR_NUMBER}
• Copy-paste ready commands for pulling and using the image
• Clear context about how to use it for local development
• Visual indicator (🐳) for easy identification

Documentation

Added comprehensive documentation in .github/scripts/README.md covering:

• How the automation works
• Benefits for reviewers and contributors
• Troubleshooting guidance
• Security and permissions model

Example Comment

## 🐳 Docker Base Image Available

A new base Docker image has been built and pushed for this PR:

**Image:** `ghcr.io/orionrobots/orionrobots-site.base:123`

### How to use this image:

```bash
# Pull the image
docker pull ghcr.io/orionrobots/orionrobots-site.base:123

# Run with the image
docker run -it ghcr.io/orionrobots/orionrobots-site.base:123 bash

## Benefits
- **Convenience**: Reviewers can quickly access Docker images without searching through workflows
- **Efficiency**: No need to dig through GitHub Package registry or workflow logs
- **Clarity**: Clear usage instructions included in every comment
- **Maintainability**: Idempotent updates prevent comment spam

## Compatibility
- Works with internal PRs and handles fork limitations appropriately
- Maintains existing workflow functionality without disruption
- Uses secure, minimal GitHub token permissions

Fixes #257.

<!-- START COPILOT CODING AGENT TIPS -->
---

✨ Let Copilot coding agent [set things up for you](https://github.com/orionrobots/orionrobots.github.io/issues/new?title=✨Set+up+Copilot+instructions&body=Configure%20instructions%20for%20this%20repository%20as%20documented%20in%20%5BBest%20practices%20for%20Copilot%20coding%20agent%20in%20your%20repository%5D%28https://gh.io/copilot-coding-agent-tips%29%0A%0A%3COnboard%20this%20repo%3E&assignees=copilot) — coding agent works faster and does higher quality work when set up for your repo.

[github-actions]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
❌ ACTION	actionlint	5		6	0	0.1s
✅ BASH	bash-exec	1		0	0	0.0s
✅ BASH	shellcheck	1		0	0	0.06s
⚠️ BASH	shfmt	1		1	0	0.0s
❌ C	cppcheck	8		8	0	0.31s
❌ CPP	cppcheck	8		8	0	0.31s
✅ JSON	npm-package-json-lint	yes		no	no	0.44s
✅ JSON	v8r	12		0	0	7.17s
❌ MARKDOWN	markdown-link-check	738		213	0	32.04s
✅ REPOSITORY	gitleaks	yes		no	no	13.94s
✅ REPOSITORY	git_diff	yes		no	no	1.43s
❌ REPOSITORY	grype	yes		2	no	33.61s
✅ REPOSITORY	secretlint	yes		no	no	43.56s
✅ REPOSITORY	syft	yes		no	no	2.04s
✅ REPOSITORY	trivy-sbom	yes		no	no	3.39s
✅ REPOSITORY	trufflehog	yes		no	no	4.81s
✅ XML	xmllint	1		0	0	192.33s
✅ YAML	v8r	13		0	0	6.83s

See detailed report in MegaLinter reports

[github-actions]

🐳 Docker Base Image Available

A new base Docker image has been built and pushed for this PR:

Image: ghcr.io/orionrobots/orionrobots-site.base:258

How to use this image:

# Pull the image
docker pull ghcr.io/orionrobots/orionrobots-site.base:258

# Run with the image
docker run -it ghcr.io/orionrobots/orionrobots-site.base:258 bash

For local development:

You can use this image as a base for testing changes without rebuilding dependencies.

This comment is automatically updated when the base image is rebuilt.