v0.5.1

• There are many new bugs and missing features. Do not use this release for important data.
• Temporarily remove group drag, image, backspace-delete, and card-level un/redo support.
• Add sub-grouping.
• Replace Electron with HTML single-file double-click distributable.
• Improve information density / compactness.
• Replace columnar scrolling with grid.
• Revise icons and add grid background.
• linear-text NPM package succeeded by Deno linear_text package.
• Move changelog.md to changelog.text.
• Total rewrite; replace React with Lit web components and NPM with Deno.