fix(web): drop the taskbar theme label, align window padding to p-2

- Taskbar: the theme toggle is icon-only now, matching the Settings
  button beside it. The theme name moves into the title/aria-label so
  an icon-only control still has an accessible name and the current
  theme stays discoverable on hover.
- Pages: Fleet, Knowledge, Learning, Ops and Signals used p-4 (or
  p-4 md:p-6) while Tasks used p-2, so windows didn't line up. All now
  p-2. App Store and Settings are deliberately untouched — they have no
  root padding, using a full-bleed header whose border spans the window;
  insetting them would break that.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/pages/Knowledge.svelte

@@ -43,7 +43,7 @@
   }
 </script>
 
-<div class="flex h-full flex-col gap-4 p-4 md:p-6">
+<div class="flex h-full flex-col gap-4 p-2">
   <div class="flex items-center justify-between">
     <h1 class="text-lg font-semibold">Knowledge</h1>
   </div>