feat(web): move Virtual displays to its own nav section; roomier preset grid

The Host page was crowded (identity, codecs, ports, GPU, displays, compositors) and the
virtual-display config surface is large enough to warrant its own home.

- New **Virtual displays** nav section: `/displays` route + `sections/Displays` (moved
  DisplayCard out of `sections/Host`), a `MonitorPlay` sidebar entry after Host, and
  `nav_displays` i18n. Removed the displays card from the Host page/view.
- On its own page the card splits into two: **Configuration** (presets + custom axes) and
  **Live displays** (the live list + arrangement table) — room to breathe.
- Presets now render in a max-2-column grid (`sm:grid-cols-2`) with larger padding, a bigger
  section heading + preset titles (text-base semibold), roomier spacing, and bottom-aligned
  "what it sets" badges so the cards line up.

web tsc + vite build + biome-lint green; deployed + verified on the Mutter box (.21).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/components/app-shell.tsx

@@ -4,6 +4,7 @@ import {
 	GaugeCircle,
 	KeyRound,
 	LibraryBig,
+	MonitorPlay,
 	ScrollText,
 	Server,
 	Settings,
@@ -21,6 +22,7 @@ const MLink = motion(Link);
 const NAV = [
 	{ to: "/", icon: Activity, label: () => m.nav_dashboard() },
 	{ to: "/host", icon: Server, label: () => m.nav_host() },
+	{ to: "/displays", icon: MonitorPlay, label: () => m.nav_displays() },
 	{ to: "/library", icon: LibraryBig, label: () => m.nav_library() },
 	{ to: "/stats", icon: GaugeCircle, label: () => m.nav_stats() },
 	{ to: "/logs", icon: ScrollText, label: () => m.nav_logs() },