feat(web): adopt cyberspace terminal aesthetic + dithered images

Rebrand light/dark themes to the cyberspace.online look: warm cream-on-black
palette (light/dark are exact inverses), self-hosted JetBrains Mono + VT323,
square corners, border-driven surfaces with no soft shadows. Adds a terminal
design-system CSS layer (DOS double-border modals with hatched corner, fg focus,
inversion-on-hover), a theme-aware <RasterImage> (Atkinson-dithered canvas with
img fallback), and unifies desktop icons, taskbar, window controls, pills and
links under one idiom. Pins window titlebars to a fixed height and switches chat
auto-scroll off scrollIntoView to avoid titlebar reflow.

VERSION 0.15.1 -> 0.16.0

web/src/lib/components/ChatThread.svelte

@@ -59,7 +59,6 @@
   } = $props()
 
   let input = $state(typeof initialDraft === 'string' ? initialDraft : '')
-  let messagesEnd = $state<HTMLDivElement | null>(null)
   let scrolledUp = $state(false)
   let container = $state<HTMLDivElement | null>(null)
 
@@ -150,12 +149,17 @@
   }
 
   // Auto-scroll to bottom on new messages (or a freshly-raised question) —
-  // unless user scrolled up to read.
+  // unless user scrolled up to read. Sets scrollTop on the messages container
+  // directly instead of `scrollIntoView`, which walks ancestors and forces a
+  // reflow that can momentarily perturb the window titlebar height.
   $effect(() => {
     void messages
     void question
     if (streaming || !scrolledUp) {
-      setTimeout(() => messagesEnd?.scrollIntoView({ behavior: 'smooth' }), 50)
+      setTimeout(
+        () => container?.scrollTo({ top: container.scrollHeight, behavior: 'smooth' }),
+        50
+      )
     }
   })
 
@@ -326,7 +330,6 @@
           {#if question}
             <OperatorQuestion {sessionId} {question} />
           {/if}
-          <div bind:this={messagesEnd}></div>
         </div>
       </div>