Fix BDD test dockerfile to use correct Node version - consolidate into serve.Dockerfile

[Copilot]

The BDD test dockerfile was using an outdated Node.js version that caused compatibility warnings with the @cucumber/cucumber dependency.

Problem

The main serve.Dockerfile uses FROM node:24-bullseye AS base, but the separate tests.Dockerfile used FROM node:18-alpine, causing this warning:

npm warn EBADENGINE Unsupported engine {
npm warn EBADENGINE   package: '@cucumber/cucumber@12.1.0',
npm warn EBADENGINE   required: { node: '20 || 22 || >=24' },
npm warn EBADENGINE   current: { node: 'v18.20.8', npm: '10.8.2' }
npm warn EBADENGINE }

Solution

• Consolidated dockerfiles: Added a new tests stage to serve.Dockerfile that inherits from the base stage (Node 24)
• Updated docker-compose: Modified the test service to use serve.Dockerfile with target: tests instead of the separate tests.Dockerfile
• Removed redundancy: Deleted tests.Dockerfile as it's no longer needed

Changes

• serve.Dockerfile: Added tests stage based on existing base stage
• docker-compose.yml: Updated test service configuration to use new target
• tests.Dockerfile: Removed (replaced by tests stage)

The BDD tests continue to work as expected via docker compose run test, with the only remaining issues being the intentionally pending step definitions. The workflow in .github/workflows/on_call_staging_test.yaml will continue to function without modification.

Fixes #231.

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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	0.05s
⚠️ BASH	shfmt	1		1	0	0.0s
❌ C	cppcheck	8		8	0	0.31s
❌ CPP	cppcheck	8		8	0	0.32s
✅ JSON	npm-package-json-lint	yes		no	no	0.44s
✅ JSON	v8r	12		0	0	7.22s
❌ MARKDOWN	markdown-link-check	736		212	0	31.35s
✅ REPOSITORY	gitleaks	yes		no	no	14.81s
✅ REPOSITORY	git_diff	yes		no	no	0.46s
✅ REPOSITORY	grype	yes		no	no	34.17s
✅ REPOSITORY	secretlint	yes		no	no	43.93s
✅ REPOSITORY	syft	yes		no	no	2.02s
✅ REPOSITORY	trivy-sbom	yes		no	no	3.32s
✅ REPOSITORY	trufflehog	yes		no	no	4.64s
✅ XML	xmllint	1		0	0	196.12s
✅ YAML	v8r	13		0	0	10.04s

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