Fix extra stats overlay visibility

[fishcharlie]

Summary

• keep the Extra Stats diagnostics visible above playback error surfaces
• preserve interactive recovery controls and context menus above diagnostics
• add regression coverage for enabling Extra Stats during a playback failure

Testing

• pnpm --filter @signalhaven/frontend exec vitest run tests/player/Player.test.tsx --reporter=verbose
• pnpm --filter @signalhaven/frontend typecheck
• pnpm --filter @signalhaven/frontend exec eslint app/_player/Player.tsx tests/player/Player.test.tsx
• pnpm exec prettier --check apps/frontend/app/_player/Player.tsx apps/frontend/tests/player/Player.test.tsx
• complete frontend suite: 454/455 passed; the unrelated TranscodingSection performance test timed out under full-suite load and passed independently

Generated using AI on behalf of Charlie Fish.