Add page transition animations and background wallpapers

Wrap page views in {#key} blocks with a fade-in animation for smooth
transitions. Add Demon Slayer wallpapers as fixed pseudo-element
backgrounds on main (Tanjiro for dashboard, Rengoku for accelerator)
with CSS crossfade. Fix section spacing lost by the page-enter wrapper
div. Minor tooltip text fixes.

ui/src/lib/UserDetailPage.svelte

@@ -232,7 +232,7 @@
                       title="View per-worker stats"
                     >{r.worker}</button>
                     {#if r.tls}
-                      <span class="badge tls" title="Connected via TLS">
+                      <span class="badge tls" title="Encrypted connection via TLS">
                         <svg viewBox="0 0 16 16" aria-hidden="true">
                           <path d="M8 1a3.5 3.5 0 0 0-3.5 3.5V7H4a1.5 1.5 0 0 0-1.5 1.5v5A1.5 1.5 0 0 0 4 15h8a1.5 1.5 0 0 0 1.5-1.5v-5A1.5 1.5 0 0 0 12 7h-.5V4.5A3.5 3.5 0 0 0 8 1Zm2 6H6V4.5a2 2 0 1 1 4 0V7Z"/>
                         </svg>
@@ -247,7 +247,7 @@
                 <td>
                   {r.hardware}
                   {#if r.openSource}
-                    <span class="oss" title="Open source hardware or firmware">★</span>
+                    <span class="oss" title="Open source hardware and firmware">★</span>
                   {/if}
                 </td>
                 <td>