chore: use .ts extensions in TypeScript imports - #405

Changed pages include:

• index.html - view
• about.html - view
• analyze-css.html - view
• ast-explorer.html - view
• baseline-overview.html - view
• blog.html - view
• css-code-quality.html - view
• css-coverage.html - view
• css-diff.html - view
• css-layers-visualizer.html - view

There are more changes not included in the list