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/app/icon.svg

@@ -1,5 +1,5 @@
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-  <path d="m4 17 6-6-6-6" stroke="#fafafa" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" fill="none" />
+  <rect width="24" height="24" rx="5" fill="#15171a" />
+  <path d="M12 19h8" stroke="#e9a857" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" fill="none" />
+  <path d="m4 17 6-6-6-6" stroke="#e9a857" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" fill="none" />
 </svg>