feat(landing,seo): Step + FooterColumn rebuild, SEO metadata, responsive hardening (#1345 #1346 #1347 #1348)

[techisigu]

Landing page: Step, FooterColumn, SEO metadata, responsive

Four landing-page issues.

What changed and why

#1345 - Step component + real "how it works" flow

• Step takes an optional href and links the step title to the corresponding feature.
  The step number is not passed in - landing.css already derives it with a CSS
  counter() from the <ol> order, so it can't drift from the visual list.
• The four steps now describe the real, shipped flow: connect a Stellar wallet -> browse
  markets -> place a bet -> claim a payout (i18n howItWorks.*), each linking to /markets
  or /account/bets.
• Tests: title links to its feature; plain title without href; no hardcoded numbering in
  the DOM; the LandingPage data-driven test asserts the <ol> and the four step links.

#1346 - FooterColumn + real footer navigation

• FooterColumn gains a children slot (for embeds) and an external link flag
  (target="_blank" + rel="noopener noreferrer").
• The footer columns were rewritten to routes that exist: Product (Markets /markets,
  Statistics /statistics, Create a market /markets/create), Resources (Documentation +
  GitHub, both external), and a "stay in the loop" column linking back to the hero signup
  form (a second <NewsletterSignup> would duplicate its field ids and break a11y). The
  dead /docs, /github (internal), /discord, /privacy, /terms links and the Legal
  column were removed - there are no such pages.
• e2e/landing-links-responsive.spec.ts asserts every internal footer link resolves
  (request.get(href) < 400) - the CI link-check the AC asks for.
• Tests: external vs internal link attributes; children render; the data-driven test now
  asserts real routes and the absence of the removed links.

#1347 - SEO metadata + structured data

• app/layout.tsx: site-wide defaults - metadataBase, a title template, Open Graph
  siteName/url, Twitter summary_large_image.
• app/page.tsx (kept server-side, still code-split via next/dynamic with ssr: true and
  the existing loading fallback): route-level title / description / canonical / full
  Open Graph + Twitter with an /og-image.png, plus an Organization + WebSite JSON-LD
  <script type="application/ld+json"> (a build-time constant, server-rendered so
  link-unfurl crawlers see it).
• Locale-specific metadata (Conditional & Chained Prediction Markets #25) is out of scope here - the i18n layer only has an en
  bundle today; SITE_URL reads NEXT_PUBLIC_SITE_URL with a default.
• Tests: landing-metadata.test.ts asserts the exported metadata shape and the layout
  defaults.

#1348 - responsive hardening

• overflow-wrap: anywhere on hero/feature/step/footer text so a long word in a translated
  locale wraps instead of widening the page.
• Grid tracks changed to minmax(min(100%, 230px), 1fr) so a track can shrink below its
  content's min-content size; .footer-content { max-width: 100% }.
• A @media (max-width: 360px) block forces single-column grids and trims inline padding.
• e2e/landing-links-responsive.spec.ts asserts scrollWidth - clientWidth <= 1 at 320 /
  768 / 1440.

How to test

cd frontend
PUPPETEER_SKIP_DOWNLOAD=true npm ci --legacy-peer-deps --ignore-scripts
./node_modules/.bin/jest src/components/__tests__/Step.test.tsx \
  src/components/__tests__/FooterColumn.test.tsx \
  src/components/__tests__/LandingPage.dataDriven.test.tsx \
  src/app/__tests__/landing-metadata.test.tsx

• 37 tests pass across the touched suites; page.test.tsx (the dynamic-loading fallback
  test) still passes - the code-split + loading spinner were preserved.
• tsc --noEmit: no errors in the touched files over the repo's pre-existing count.
• e2e/landing-links-responsive.spec.ts not run here (needs the browser install).
• Pre-existing on main, unchanged by this branch (verified against a clean upstream/main
  worktree - identical 30 failures): Statistics.test.tsx, LandingPage.keyboard.test.tsx,
  LandingPage.accessibility.test.tsx, useAsync.test.ts, useReferral.test.ts.

Breaking changes

None. New props and metadata only. Footer link targets changed (removed dead links).

Related issues

Closes #1345
Closes #1346
Closes #1347
Closes #1348

PR Checklist

• Branch is up to date with main
• Commit messages follow Conventional Commits
• Tests added or updated for the change
• Documentation updated if behaviour changed (n/a)
• No secrets or credentials committed

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