fix(outreach): use the blog title in metadata

[jiangyuer018]

Summary

Before this change, the blog index used the site title for both parts of its metadata title, so English and French pages showed a duplicated site name.

This change uses the existing localized blog.title key for the first part and keeps meta.title for the site name.

Closes #1775

Validation

• Confirmed blog.title provides Blog and Blogue in apps/outreach/src/i18n/translations/blog.json.
• git diff --check passed.
• The outreach package has no test suite, as documented in apps/outreach/AGENTS.md.
• The Astro build was not run because dependencies are not installed and the checkout's Node version is below the repository minimum.