Restyle the UI: instrument-panel palette, type system, and a signal accent

Replaces the default shadcn grayscale/Geist look with a deliberate
identity built around the product's own subject - a control panel for
running scripts and watching their output live:

- Type: Bricolage Grotesque for page/card titles (via the existing
  --font-heading token, used with restraint), IBM Plex Sans for UI body
  text, IBM Plex Mono for technical data (run IDs, commands, timestamps,
  status labels) - all self-hosted at build time via next/font/google,
  no runtime CDN dependency for a self-hosted tool.
- Color: a cool graphite ink/paper base with a warm brass signal accent
  in both themes. The brass tone doubles as the "running" status color,
  so an active run literally lights the UI up with the brand color.
  New --status-* tokens give queued/running/succeeded/failed/cancelled/
  warn a single source of truth instead of ad-hoc Tailwind color classes.
- Structural language: small tracked-out uppercase mono labels mark
  technical fields (Command, Variables, Triggered by...) consistently;
  the live-output terminal gets an instrument-bezel frame (header bar +
  panel) instead of floating loose above the xterm canvas.

Layout/IA is unchanged throughout - this is a token- and detail-level
pass, not a restructuring.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/layout/nav.tsx

@@ -34,9 +34,9 @@ export function Nav({
         <div className="flex min-w-0 items-center gap-3 sm:gap-6">
           <Link
             href="/"
-            className="flex shrink-0 items-center gap-2 font-semibold tracking-tight"
+            className="font-heading flex shrink-0 items-center gap-2 text-[1.05rem] font-semibold tracking-tight"
           >
-            <Terminal className="size-5" />
+            <Terminal className="text-primary size-5" />
             TriggerShell
           </Link>
           <nav className="flex items-center gap-1">
@@ -45,8 +45,8 @@ export function Nav({
                 key={href}
                 href={href}
                 className={cn(
-                  "text-muted-foreground hover:text-foreground flex items-center gap-1.5 rounded-md px-2 py-1.5 text-sm font-medium transition-colors sm:px-3",
-                  pathname === href && "bg-muted text-foreground",
+                  "text-muted-foreground hover:text-foreground hover:bg-muted/60 flex items-center gap-1.5 rounded-md px-2 py-1.5 text-sm font-medium transition-colors sm:px-3",
+                  pathname === href && "bg-primary/10 text-foreground",
                 )}
               >
                 <Icon className="size-4" />