feat(seo): add hreflang tags, canonical URLs, and central Seo helper

[sanusishafii989]

Summary

Adds hreflang alternates, self-referencing canonical URLs, and consistent OG/Twitter metadata across all 18 pages via a central <Seo> component.

Changes

• Create src/utils/seo.tsx — reusable <Seo> component that emits canonical URL, hreflang alternates (en, es, x-default), OG tags, and Twitter Card metadata using useLocation() for self-referencing canonicals
• Add /es/* locale-prefixed routes in App.tsx via LocaleSetter wrapper so /es/faq, /es/grants, etc. render with Spanish locale
• Audit all 18 pages: every route now has title, description, canonical, hreflang, og:, and twitter: metadata
• Replace ad-hoc Helmet blocks on About, Blog, Careers, Ecosystem, Stellar with centralized <Seo> component
• Add SEO metadata to 12 pages that previously had none: Faq, Privacy, Newsletter, UseCases, Roadmap, Grants, CaseStudies, Contributors, Vitals, NotFound, Press, Home
• Add /es/* routes to sitemap knownRoutes

Acceptance Criteria

• Every route emits absolute production canonical URL
• Every localized route emits hreflang alternates for en, es, x-default
• /es/faq renders the FAQ page (not NotFound) — via LocaleSetter
• Build passes (zero TypeScript errors)
• Lighthouse SEO ≥ 90 (CI confirmed)

Closes #125

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[sanusishafii989]

Rebased onto latest develop to resolve the Blog.tsx conflict from #136. The <Seo> component now sits alongside the new BlogToc and max-w-5xl layout without issues.

[truthixify]

Heads up: this went conflicted a few minutes ago because #142, #143 and #146 landed on develop. It was mergeable right before that, so nothing is wrong with your work.

git fetch origin
git rebase origin/develop

and it should be good to go.

[truthixify]

Context for this one is on #139, worth reading there.

Short version: your fork's develop (which is #139's head) contains this PR's commit as well, so the two conflict with each other before they even reach develop.

The blocker here specifically: this replaces <Helmet> with the central <Seo> component across Blog.tsx, CaseStudies.tsx, Faq.tsx and App.tsx, and #140 has since added JSON-LD <script> blocks to those same pages. Resolving means deciding how the two compose, either <Seo> accepts the structured data and renders it, or the pages keep a separate script tag next to it. Your call on your own abstraction, so I left it.

The generated public/feed.xml and public/sitemap.xml conflicts you can ignore, just regenerate with pnpm build after resolving the source files.