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/index.css

@@ -93,6 +93,19 @@
   --blink-dur: 2s;
   --pulse-dur: 1s;
   --spin-dur:  1.5s;
+
+  /* ── Accent swap (matrix default) ──────────────── */
+  --accent:         var(--matrix);
+  --accent-tint-10: var(--matrix-tint-10);
+  --accent-tint-30: var(--matrix-tint-30);
+  --accent-glow:    var(--matrix-glow);
+}
+
+html[data-accent="violet"] {
+  --accent:         var(--violet);
+  --accent-tint-10: var(--violet-tint-10);
+  --accent-tint-30: rgba(238, 130, 238, 0.30);
+  --accent-glow:    var(--violet-glow);
 }
 
 *, *::before, *::after {