Add TypeScript Props interfaces to improve type safety:
- Tags.astro: tags and class props
- SocialShare.astro: text, url (string|URL), and class props
- GridItem.astro: post prop with BlogPost type
- ListItem.astro: post prop with BlogPost type
- SinglePost.astro: post (with optional body) and url props

Also fixed pre-existing issues:
- Handle Date|string for datetime attributes via conversion
- Handle optional readingTime with nullish coalescing
- Support URL type for url props (matches getCanonical return type)
- Remove HTML comments from JSX blocks (Prettier compatibility)