Add a dynamic sitemap and per-page metadata for marketplace, commitments, and create routes

[1nonlypiece]

📌 Description

src/app/sitemap.ts exists but the app lacks complete per-route metadata
(titles, descriptions, Open Graph/Twitter tags) for the marketplace, commitments,
create, and settings routes. This weakens shareability and SEO of the public
surfaces.

This issue adds per-route metadata exports and ensures the sitemap covers all
public routes.

🎯 Requirements and Context

• Add metadata (title, description, OG/Twitter) to public route segments.
• Ensure src/app/sitemap.ts enumerates current public routes.
• Keep wallet-gated/private routes out of the sitemap.
• Validate metadata renders without hydration issues.

🛠️ Suggested Execution

1. Fork the repo and create a branch

git checkout -b docs/route-metadata-sitemap

2. Implement changes

• Add metadata to marketplace, commitments, create, and settings route
  files; update src/app/sitemap.ts.
• Add src/app/sitemap.test.ts asserting the sitemap includes the expected
  public routes and excludes private ones.
• Add docs/SEO_METADATA.md documenting the metadata conventions.
• Validate metadata output for a couple of routes.

3. Test and commit

• Run pnpm test.
• Cover edge cases: new route added (drift), private route excluded, missing
  description fallback.

Example commit message

docs: per-route metadata and complete dynamic sitemap

✅ Guidelines

• Minimum 95% test coverage on the sitemap helper.
• Clear, reviewer-friendly documentation.
• Timeframe: 96 hours.

🏷️ Labels

type-documentation · type-enhancement · area-frontend · MAYBE REWARDED ·
GRANTFOX OSS · OFFICIAL CAMPAIGN

💬 Community & Support

• Join the CommitLabs contributor Discord to coordinate and get unblocked fast:
  https://discord.gg/WV7tdYkJk
• Introduce yourself before starting so we can avoid duplicate work and pair you
  with a reviewer. Maintainers triage actively and review fast.