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/index.html

@@ -4,12 +4,6 @@
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>Oikos</title>
-    <link rel="preconnect" href="https://fonts.googleapis.com" />
-    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
-    <link
-      href="https://fonts.googleapis.com/css2?family=DM+Sans:ital,opsz,wght@0,9..40,100..1000;1,9..40,100..1000&family=DM+Mono:ital,wght@0,300;0,400;0,500;1,300;1,400;1,500&family=Inknut+Antiqua:wght@300;400;500;600;700&display=swap"
-      rel="stylesheet"
-    />
     <link rel="icon" type="image/svg+xml" href="favicon.svg" />
     <link rel="apple-touch-icon" href="apple-touch-icon.png" />
     <link rel="icon" type="image/png" sizes="192x192" href="android-chrome-192.png" />