[codex] remove rendered key attributes from tags

[Sean-Kenneth-Doherty]

Summary:

• Remove React-style key attributes from rendered project tag wrappers.
• Keep the existing tag markup and styling otherwise unchanged.

Validation:

• Source scan found no remaining key attributes in Astro components/pages/layouts.
• pnpm build
• git diff --check main...HEAD
• Built HTML scan found no rendered key attributes in dist/index.html or the guide page, then generated output was restored.

Refs #347.

[Sean-Kenneth-Doherty]

Fresh local validation against the detached PR head (c969c2a):

• GITHUB_TOKEN=$(gh auth token) pnpm build -> Astro build succeeded, 2 pages
• git diff --check -> clean
• confirmed src/components/ProjectCard.astro no longer renders key={tag} on tag <div> elements
• checked generated dist/index.html and dist/contribute-to-opensource/index.html for no rendered key/data-astro-key tag artifacts

Validation ran in a scratch detached worktree so the main checkout was not touched.