[codex] add Mermaid to project suggestions

[Sean-Kenneth-Doherty]

Summary

• add Mermaid to the project suggestions list
• link the card to the Mermaid GitHub contributor page
• include GitHub avatar, concise description, and diagram/visualization tags

Validation

• GitHub API reports mermaid-js/mermaid is public, unarchived, and on develop
• https://github.com/mermaid-js/mermaid/contribute returns HTTP 200
• https://avatars.githubusercontent.com/u/57169982?v=4 returns HTTP 200
• mermaid-js/mermaid has open Good first issue-labeled issues
• Mermaid source count is 1 via src/data/projects.js import
• git diff --check
• GITHUB_TOKEN=$(gh auth token) pnpm build
• generated dist/index.html contained the Mermaid card and contributor link before restoring generated files

Addresses #1

[Sean-Kenneth-Doherty]

Validated locally on head 2ef58dfe430219cca533dd36c18935c530329aa4 in an isolated worktree:

• gh api repos/mermaid-js/mermaid --jq ... confirmed the repo is public, unarchived, and on develop
• gh search issues --repo mermaid-js/mermaid --state open --label "Good first issue!" --limit 3 --json number,title --jq "length" returned 3
• imported src/data/projects.js and confirmed the Mermaid source count is 1 with the expected contributor link and avatar
• curl -L returned HTTP 200 for https://github.com/mermaid-js/mermaid/contribute
• curl -L returned HTTP 200 for https://avatars.githubusercontent.com/u/57169982?v=4
• git diff --check origin/main...HEAD && git diff --check
• GITHUB_TOKEN=$(gh auth token) pnpm build
• checked generated dist/index.html before restoring generated files; the Mermaid card is present and the contributor link appears once

All passed. Note: the repo label is Good first issue! with an exclamation mark; querying good first issue without it returned 0. gh pr checks reports no hosted checks on this branch.

[Sean-Kenneth-Doherty]

Closing this to reduce maintainer review noise from my project-suggestion-only PR batch. I am pruning these so the queue can focus on concrete bug, security, accessibility, and performance fixes.