[codex] Refresh learning workbench styling

[greenthree]

Summary

• Rework the learning page into the green-and-white training workbench direction.
• Add the coordinate-grid hero treatment, denser section structure, responsive knowledge map, platform cards, and consistent selected states while keeping the existing DOM and interactions.
• Fix the WCAG AA contrast failure on inactive week-tab descriptions by removing the inherited opacity.

Validation

• npx prettier --check src/pages/learning.css
• git diff --check
• npx playwright test e2e/accessibility.spec.ts --grep "learning has no automatically" (5/5 projects)
• npm run lint
• npm test (98 files, 637 tests)
• npm run build
• Chrome checks at desktop and 390px mobile viewports: no overflow, framework overlay, or relevant console errors; week-tab interaction verified.

Notes

• Production was not changed.
• The full 200-test Playwright matrix was not rerun in this pass; its only prior failures were the five duplicated axe checks above, now passing after the minimal CSS fix.