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/desktop-shell/Taskbar.svelte

@@ -53,10 +53,10 @@
   }
 </script>
 
-<div class="flex h-11 shrink-0 items-center gap-1.5 border-t bg-muted/30 px-2">
+<div class="flex h-11 shrink-0 items-center gap-1.5 border-t border-border bg-background px-2">
   <button
     type="button"
-    class="flex shrink-0 items-center justify-center rounded-md p-1.5 text-muted-foreground hover:bg-muted hover:text-foreground"
+    class="flex shrink-0 items-center justify-center border border-border p-1.5 text-muted-foreground transition-colors hover:border-foreground hover:bg-foreground hover:text-background"
     onclick={toggleShowDesktop}
     title="Show desktop"
   >
@@ -65,7 +65,7 @@
 
   <div class="h-6 w-px shrink-0 bg-border"></div>
 
-  <div class="flex min-w-0 flex-1 items-center gap-1 overflow-x-auto">
+  <div class="flex min-w-0 flex-1 items-center gap-1 overflow-x-auto py-1.5">
     {#each buttons as win (win.id)}
       {@const Icon = iconFor(win.id)}
       {@const badge = badgeFor(win.id)}
@@ -73,12 +73,12 @@
         <button
           type="button"
           data-taskbar-btn={win.id}
-          class="flex h-8 max-w-56 items-center gap-1.5 rounded-md border px-2 font-mono text-xs transition-colors {$wmState.focusedId ===
+          class="flex h-8 max-w-56 items-center gap-1.5 border px-2 font-mono text-xs transition-colors {$wmState.focusedId ===
             win.id && win.stage !== 'minimized'
-            ? 'border-primary/50 bg-primary/10 text-foreground'
-            : 'border-transparent bg-card/60 text-muted-foreground hover:bg-muted'} {win.stage ===
+            ? 'border-foreground bg-foreground text-background'
+            : 'border-border bg-background text-muted-foreground hover:border-foreground hover:bg-foreground hover:text-background'} {win.stage ===
           'minimized'
-            ? 'opacity-60'
+            ? 'opacity-50'
             : ''}"
           onclick={() => toggle(win.id, win)}
           title={win.title}
@@ -87,7 +87,7 @@
           <span class="min-w-0 truncate">{truncateMiddle(win.title, 26)}</span>
           {#if badge > 0}
             <span
-              class="flex h-3.5 min-w-3.5 shrink-0 items-center justify-center rounded-full bg-destructive px-1 text-[9px] font-semibold text-destructive-foreground"
+              class="flex h-3.5 min-w-3.5 shrink-0 items-center justify-center border border-background bg-destructive px-1 text-[9px] font-semibold text-destructive-foreground"
             >
               {badge > 99 ? '99+' : badge}
             </span>
@@ -95,7 +95,7 @@
         </button>
         <button
           type="button"
-          class="absolute -top-1.5 -right-1.5 hidden size-4 items-center justify-center rounded-full bg-muted-foreground/80 text-background hover:bg-destructive group-hover/tb:flex"
+          class="win-ctrl absolute -top-1.5 -right-1.5 hidden size-4 group-hover/tb:flex"
           onclick={(e) => {
             e.stopPropagation()
             wm.close(win.id)
@@ -113,7 +113,7 @@
   <div class="flex shrink-0 items-center gap-0.5">
     <button
       type="button"
-      class="flex items-center justify-center rounded-md p-1.5 text-muted-foreground hover:bg-muted hover:text-foreground"
+      class="flex items-center justify-center border border-border p-1.5 text-muted-foreground transition-colors hover:border-foreground hover:bg-foreground hover:text-background"
       onclick={() => toggleTheme()}
       title="Cycle theme ({THEME_LABELS[getTheme()]})"
       aria-label="Cycle theme, currently {THEME_LABELS[getTheme()]}"
@@ -122,12 +122,12 @@
     </button>
     <button
       type="button"
-      class="flex items-center justify-center rounded-md p-1.5 text-muted-foreground hover:bg-muted hover:text-foreground"
+      class="flex items-center justify-center border border-border p-1.5 text-muted-foreground transition-colors hover:border-foreground hover:bg-foreground hover:text-background"
       onclick={() => openAppWindow('settings')}
       title="Settings"
     >
       <SettingsIcon class="size-4" />
     </button>
-    <span class="px-1.5 text-[11px] text-muted-foreground select-none">{VERSION}</span>
+    <span class="px-1.5 font-mono text-[11px] text-muted-foreground select-none">{VERSION}</span>
   </div>
 </div>