Overhaul blocking-route dev overlay for clarity and actionability
- Centralize console error strings in blocking-route-messages.ts
- Add interactive decision-tree guidance with collapsible sections
- Use native HTML <details>/<summary> for accessible collapsibles
- Extract error detection logic into blocking-route-error-details.ts
- Extract old-style description components into blocking-route-descriptions.tsx
- Add per-fix documentation links to nextjs.org/docs/messages
- Extract specific API names (e.g. cookies()) from error messages