Public landing page redesign and public credit market data

**Title:** Public landing page redesign and public credit market data

**Description:**
Implement the public-facing redesign scoped by the spike #4638. Rebuild `/public` into a BC Government–branded program storefront with an aggregated, anonymized credit-market snapshot, add a dedicated public **Credit market data** page, surface the existing public tools, and keep BCeID/IDIR login one click away.

**Purpose and benefit to user:**
Members of the public (industry, media, researchers, prospective suppliers) can understand what the Low Carbon Fuel Standard is, see how the program and credit market are performing (aggregate and anonymized), and reach the public tools without logging in. Fuel suppliers and government staff retain clear login entry points and the existing auth flow.

**Acceptance Criteria:**
- [ ] Given I am an unauthenticated visitor, when I open `/public`, then I see a BC Gov–branded landing page with program context, at-a-glance stats, a credit-market snapshot, and the public tools.
- [ ] Given I am an unauthenticated visitor, when I open the app root, then I land on the public page (not the login screen).
- [ ] Given I am any visitor, when I view credit-market data, then only aggregated, anonymized figures are shown — periods with fewer than 5 transfers or 3 participating organizations are withheld, and no individual prices or organizations are exposed.
- [ ] Given I am a visitor, when I select "Explore the full market data", then I reach a dedicated `/market-data` page with KPIs, a price/volume chart, quarterly/annual report tables, and CSV export.
- [ ] Given I am a fuel supplier or government analyst, when I am on the public pages, then BCeID and IDIR login are clearly available and the existing auth flow works.

**Development Checklist:**
- [ ] Backend `credit_market` aggregation module: government overview + public snapshot + public report (with k-anonymity suppression)
- [ ] Public landing page redesign (BC Gov header/hero, snapshot card, tools list, legislation links, login CTA)
- [ ] Public `/market-data` page (KPIs, charts, report tables, CSV export)
- [ ] Root routing so logged-out visitors land on the public page
- [ ] Compliance unit calculator restyled to the BC Gov palette
- [ ] Unit tests (backend aggregation + frontend views)
- [ ] Accessibility (WCAG) and responsive review
- [ ] French translations for new public copy

**Notes:**
- Implemented in PR #4639 (branch `feat/alex-credit-market-index`).
- Spike: #4638.
- Outstanding follow-ups: French translations, full WCAG audit, and optional server-side CSV export.