feat(web): command palette, toasts, and global shell chrome

- CommandPalette (Alt+K): fuzzy action launcher with keyboard nav.
- Toasts: ephemeral notification stack + provider.
- useGlobalHotkeys: Alt+K palette toggle, G-chord navigation
  (G D/F/M/L/B/A/S/U/E/C), respects editable-element focus.
- Layout/App: wire ToastProvider at root, mount the palette inside the
  authed shell, introduce the global search box in the top bar.
- MazeNETRoute now renders TopologyList inline when no ?topology is
  present, instead of bouncing through a redirect.
- index.css: a few global token tweaks consumed by the new chrome.

Fixes a latent breakage: Config.tsx and MazeNET already imported
./Toasts/useToast but the directory was never committed.

decnet_web/src/components/Toasts/toast-context.ts

@@ -0,0 +1,19 @@
+import { createContext } from 'react';
+
+export type ToastTone = 'matrix' | 'violet' | 'alert';
+
+export interface ToastInput {
+  text: string;
+  icon?: string;
+  tone?: ToastTone;
+}
+
+export interface Toast extends ToastInput {
+  id: number;
+}
+
+export interface ToastContextValue {
+  push: (t: ToastInput) => void;
+}
+
+export const ToastContext = createContext<ToastContextValue | null>(null);