Prepare codebase for migration to Coves backend by excluding legacy code from type checking while fixing remaining TypeScript errors in active code. Changes: - Exclude legacy markdown, piefed, and lemmy/adapter from tsconfig and eslint - Add @ts-nocheck to legacy files pending migration - Update pnpm check to use --diagnostic-sources and --threshold error - Fix Button.svelte Props interface to use explicit props with index signature - Update UserAutocomplete.onselect to accept optional Person - Add Icon prop type declarations to app.d.ts - Remove unused props from CommentItem, ProfileButton, RemoveModal - Fix CommunityLink Icon title accessibility (wrap in span) - Replace deprecated preventDefault import in ImagePreviewInput - Add class prop to Tabs and PostIframe components - Use $derived instead of $state for derived values in saved/signup pages - Add DEFAULT_CLIENT_TYPE to validateInstance calls - Fix route paths to consistently use [id=integer] matcher - Simplify navigation using template literals Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>