Rename serve.Dockerfile to Dockerfile and update all references

[Copilot]

The serve.Dockerfile has evolved to include multiple stages and targets serving various purposes in the project. The name no longer accurately reflects its broader functionality, so it has been renamed to the more conventional Dockerfile.

Changes Made

• Renamed serve.Dockerfile to Dockerfile
• Updated all 9 references in docker-compose.yml to use the new filename
• Updated the GitHub workflow trigger path in .github/workflows/on_pr_test.yaml
• Added Dockerfile to .eleventyignore to prevent it from being included in the built site

Validation

All Docker Compose services continue to work correctly with the new filename:

• serve - Development server
• dist - Build distribution
• build - Eleventy build
• test - BDD testing
• shell - Debug shell
• http_serve - Apache server
• broken_links - Link checker
• staging - Staging environment

The Dockerfile syntax and all multi-stage build targets remain unchanged, ensuring full backward compatibility while providing a cleaner, more standard naming convention.

Fixes #233.

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[github-actions]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
❌ ACTION	actionlint	5		6	0	0.08s
✅ 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	0.3s
✅ JSON	npm-package-json-lint	yes		no	no	0.46s
✅ JSON	v8r	12		0	0	7.77s
❌ MARKDOWN	markdown-link-check	736		212	0	36.3s
✅ REPOSITORY	gitleaks	yes		no	no	13.52s
✅ REPOSITORY	git_diff	yes		no	no	1.05s
✅ REPOSITORY	grype	yes		no	no	35.66s
✅ REPOSITORY	secretlint	yes		no	no	42.94s
✅ REPOSITORY	syft	yes		no	no	1.65s
✅ REPOSITORY	trivy-sbom	yes		no	no	3.34s
✅ REPOSITORY	trufflehog	yes		no	no	4.5s
✅ XML	xmllint	1		0	0	192.79s
✅ YAML	v8r	13		0	0	6.39s

See detailed report in MegaLinter reports