#7 SEO/UX: normalize post URLs to use readable canonical slugs

Some post links are still rendered with encoded hyphen sequences in the HTML, for example: - `/posts/the%2Dcommodore%2D64%2Dand%2Dhow%2Dit%2Dhas%2Daffected%2Dprogrammers%2Dtoday` - `/posts/ai%2Dand%2Dthe%2Dfuture%2Dof%2Dthe%2Dweb` Suggested fix: - Emit human-readable canonical slugs in templates - Keep redirects for older encoded links so nothing breaks - Add/confirm canonical tags for the public post pages Why this matters: - Better shareability and readability - Cleaner social previews and search results - Reduces confusion when copying links from the site