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/ToastProvider.tsx

@@ -0,0 +1,33 @@
+import React, { useCallback, useEffect, useRef, useState } from 'react';
+import Toasts from './Toasts';
+import { ToastContext } from './toast-context';
+import type { Toast, ToastInput } from './toast-context';
+
+const DISMISS_MS = 3200;
+
+export const ToastProvider: React.FC<{ children: React.ReactNode }> = ({ children }) => {
+  const [items, setItems] = useState<Toast[]>([]);
+  const timers = useRef<Map<number, ReturnType<typeof setTimeout>>>(new Map());
+
+  const push = useCallback((t: ToastInput) => {
+    const id = Date.now() + Math.random();
+    setItems(prev => [...prev, { ...t, id }]);
+    const timer = setTimeout(() => {
+      setItems(prev => prev.filter(x => x.id !== id));
+      timers.current.delete(id);
+    }, DISMISS_MS);
+    timers.current.set(id, timer);
+  }, []);
+
+  useEffect(() => {
+    const map = timers.current;
+    return () => { map.forEach(clearTimeout); map.clear(); };
+  }, []);
+
+  return (
+    <ToastContext.Provider value={{ push }}>
+      {children}
+      <Toasts items={items} />
+    </ToastContext.Provider>
+  );
+};