fix: resolve TypeScript build errors and add E2E test

- Fix type annotations in App.tsx (setTabs callback)
- Cast restoreWikilinksInBlocks result in Editor.tsx for BlockNote compatibility
- Fix vi.fn() mock types in useAutoSave.test.ts
- Add E2E test verifying editor loads and renders note content
- Update .claude-done with editor-save-bug summary

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/Editor.tsx

@@ -290,7 +290,7 @@ export const Editor = memo(function Editor({
     // Convert blocks → markdown, restoring wikilinks first
     const blocks = editor.document
     const restored = restoreWikilinksInBlocks(blocks)
-    const bodyMarkdown = editor.blocksToMarkdownLossy(restored)
+    const bodyMarkdown = editor.blocksToMarkdownLossy(restored as typeof blocks)
 
     // Reconstruct the full file: preserve original frontmatter + title heading
     const [frontmatter] = splitFrontmatter(tab.content)