fix(feature-page): clarify browser availability in WPT cards

[xianjianlf2]

Fixes #2548

Feature-page WPT cards now show an explicit Available/Not available status before the score, using the existing status icons and color tokens. The score is labeled as WPT score, and an available browser without WPT data shows No score instead of N/A so it cannot be mistaken for lack of browser support.

Validation:

• npm --prefix frontend run build
• npx prettier --check frontend/src/static/js/components/webstatus-feature-page.ts frontend/src/static/js/components/test/webstatus-feature-page.test.ts
• npx eslint src/static/js/components/webstatus-feature-page.ts src/static/js/components/test/webstatus-feature-page.test.ts
• npx lit-analyzer src/static/js/components/webstatus-feature-page.ts
• Chromium component tests: 30 passed

[xianjianlf2]

Synced this PR with the current main in 6deda57a (the branch had fallen 74 commits behind); the merge completed without conflicts.

Validation on Node 24:

• frontend Prettier, ESLint, Lit Analyzer, and TypeScript checks passed
• frontend production build passed
• targeted webstatus-feature-page suite passed in Chromium (30 tests)

The upstream build and Dependabot tidy workflows are currently waiting for maintainer approval (action_required). @rviscomi, could you please approve the workflows and review this fix when convenient?