Replace hand-authored social icons with verified open-source SVGs

github/orcid/mastodon/bluesky/matrix: official Simple Icons paths
(CC0), fetched from simple-icons/simple-icons. linkedin: Simple Icons
no longer includes it (removed from the project entirely, likely a
brand/legal request), so sourced from Tabler Icons' brand-linkedin
(filled variant, MIT license) instead for a closer visual match to
the other filled-style icons than their outline variant.

Previous icons were reconstructed from memory as an approximation,
not verified against any actual licensed source.

templates/icons/bluesky.svg

@@ -1 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" role="img" aria-hidden="true" focusable="false"><path fill="currentColor" d="M12 10.8c-1.087-2.114-4.046-6.053-6.798-7.995C2.566.944 1.561 1.266.902 1.565.139 1.912 0 3.283 0 4.088c0 .805.444 6.578.734 7.552.96 3.213 4.373 4.303 7.53 3.95-4.579.664-8.639 2.284-3.307 8.598 6.03 6.828 8.269-1.463 9.438-5.594 1.17 4.13 2.65 12.185 9.339 5.594 5.05-5.594 1.32-7.934-3.259-8.598 3.157.353 6.57-.737 7.53-3.95.29-.974.734-6.746.734-7.552 0-.805-.14-2.176-.902-2.523-.66-.3-1.664-.622-4.301 1.24C16.046 4.747 13.087 8.686 12 10.8z"/></svg>
+<svg role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg" fill="currentColor" aria-hidden="true" focusable="false"><title>Bluesky</title><path d="M5.202 2.857C7.954 4.922 10.913 9.11 12 11.358c1.087-2.247 4.046-6.436 6.798-8.501C20.783 1.366 24 .213 24 3.883c0 .732-.42 6.156-.667 7.037-.856 3.061-3.978 3.842-6.755 3.37 4.854.826 6.089 3.562 3.422 6.299-5.065 5.196-7.28-1.304-7.847-2.97-.104-.305-.152-.448-.153-.327 0-.121-.05.022-.153.327-.568 1.666-2.782 8.166-7.847 2.97-2.667-2.737-1.432-5.473 3.422-6.3-2.777.473-5.899-.308-6.755-3.369C.42 10.04 0 4.615 0 3.883c0-3.67 3.217-2.517 5.202-1.026"/></svg>