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/stores/theme.svelte.ts

@@ -42,6 +42,6 @@ export function toggleTheme(): Theme {
 }
 
 export const THEME_LABELS: Record<Theme, string> = {
-  light: 'Terracotta',
-  dark: 'Carbon'
+  light: 'Light',
+  dark: 'Dark'
 }