Redesign metadata, viewport, and sync IO error overlays
- Extract shared guidance components (DocsLink, FixDiff, ErrorExplanation)
- Add MetadataViewportGuidance with Elm-style explanation and collapsible fixes
- Add SyncIOGuidance for Math.random/Date.now/crypto errors (server + client)
- Restructure metadata/viewport build messages to Cause/Fix format
- Restructure sync IO build messages to Cause/Fix format
- Add targeted doc anchors for all "Learn more" links
- Add description frontmatter to 11 error doc pages
- Labels: "Metadata Blocks Loading", "Viewport Blocks Loading", "Non-deterministic API"
Made-with: Cursor
