UI: drop tab-bar tap highlight; don't slide the first screen on launch

Tab bar: tapping a bottom-tab icon flashed a background — the icon square's
:active press tint plus the default WebKit tap flash, the same pair removed from
the lobby rows. Drop the press tint and set -webkit-tap-highlight-color:
transparent on .tab. The selected-tab highlight (Settings / Comms hubs) stays.

Startup slide: the route pane's in:slideX is local to its {#key} block, so it
plays on that block's own first mount when app.ready flips — the lobby slid in on
launch as if navigated into from another screen. Gate the slide duration to 0 for
the first pane shown after boot (a `started` flag set right after it mounts), so
launch is static while every later route change animates as before.

ui/src/components/TabBar.svelte

@@ -34,12 +34,13 @@
     width: 100%;
     user-select: none;
     -webkit-user-select: none;
+    -webkit-tap-highlight-color: transparent; /* no WebKit flash on tap */
   }
   :global(.tab:disabled) {
     opacity: 0.4;
   }
-  /* The icon square hugs the emoji (just a little padding) so it is the press-highlight
-     target and the badge can sit on its corner. */
+  /* The icon square hugs the emoji (just a little padding) so the badge can sit on its
+     corner. */
   :global(.tab .sq) {
     position: relative;
     display: inline-grid;
@@ -50,12 +51,9 @@
     line-height: 1;
     transition: background-color 0.12s;
   }
-  :global(.tab:active:not(:disabled) .sq) {
-    background: var(--surface-2);
-  }
   /* A tab that navigates between peer views (Settings / Comms hubs) stays highlighted
-     while selected: a filled square with an accent underline, distinct from the
-     momentary press tint above. */
+     while selected: a filled square with an accent underline. A tap itself leaves no
+     highlight — there is no press tint, and the WebKit tap flash is disabled on .tab. */
   :global(.tab.active .sq) {
     background: var(--surface-2);
     box-shadow: inset 0 -2px 0 var(--accent);