feat(verification): add Mermaid support for Docker-based verification

[apoorv7g]

Adds Mermaid to the Docker verification pipeline so generated .mmd diagrams from the corpus are syntax-checked in CI and locally, consistent with other codegen targets.

Changes

• Register mermaid in verification/docker/targets.json with Mermaid CLI target and mermaid.parse validation tool.
• Add a Mermaid verification Docker image (verification/docker/mermaid/) that generates diagrams via run-case.sh and validates each .mmd with mermaid.parse (via jsdom for Node DOM APIs).
• Add verification/docker/mermaid/validate.js with a shared parseMermaid() helper used by both Docker and unit tests.
• Add test/verification/mermaid.validate.test.js to run corpus cases through MermaidVisitor and assert every generated .mmd parses.
• Wire Mermaid into CI: verify-codegen.yml matrix, scripts/verification/docker-run.js targets list, and verify:docker:mermaid npm script.
• Add mermaid@11.12.0 and jsdom@25.0.1 as devDependencies for local test validation.

Flags

• Mermaid’s parser expects browser DOM APIs; validation installs a minimal jsdom environment before calling mermaid.parse.
• The Docker image installs mermaid and jsdom under /opt/mermaid-verify (next to validate.js) so ESM import resolution works; NODE_PATH alone is insufficient for ESM.
• Mermaid and jsdom versions are pinned to match between the Docker image and package.json devDependencies.

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname

[apoorv7g]

@DianaLease @ekarademir Review for this PR whenever possible( but a little quick :))