feat(web): Webhooks page + ALERTS nav group

New /webhooks admin page with table-based subscription management:
- CREATE WEBHOOK (inline form row — no modal) with simple-event
  checkboxes (AttackerDetail / DeckyStatus / SystemStatus) that
  expand to bus-topic patterns server-side, and an advanced-mode
  textarea for raw NATS-style patterns.
- Bulk-select + DELETE SELECTED with two-click arm pattern.
- Per-row test-ping (zap), pencil edit, and delete actions.
- Last-fired timestamp column.
- Yellow banner surfacing insecure_url warnings (WH-03): http:// is
  allowed but flagged so operators see it on every page load.
- Post-create secret modal — the secret is shown exactly once with
  a COPY button and a clear "won't see this again" notice.

Sidebar nav regrouped: /live-logs and /webhooks now live under a new
ALERTS NavGroup (Bell icon). The alertCount badge rides the Live
Logs sub-item. Command palette gains a "Webhooks" GO TO entry with
the `G W` chord.

Side-fix: useFocusSearch.ts was failing the build under
verbatimModuleSyntax (pre-existing, unrelated). Split the React
import to satisfy tsc; no behavioural change.

decnet_web/src/App.tsx

@@ -5,6 +5,7 @@ import Layout from './components/Layout';
 import Dashboard from './components/Dashboard';
 import DeckyFleet from './components/DeckyFleet';
 import LiveLogs from './components/LiveLogs';
+import Webhooks from './components/Webhooks';
 import Attackers from './components/Attackers';
 import AttackerDetail from './components/AttackerDetail';
 import Config from './components/Config';
@@ -80,6 +81,7 @@ const AuthedShell: React.FC<AuthedShellProps> = ({ onLogout, onSearch, searchQue
           <Route path="/topologies" element={<Navigate to="/mazenet" replace />} />
           <Route path="/mazenet" element={<MazeNETRoute />} />
           <Route path="/live-logs" element={<LiveLogs />} />
+          <Route path="/webhooks" element={<Webhooks />} />
           <Route path="/bounty" element={<Bounty />} />
           <Route path="/attackers" element={<Attackers />} />
           <Route path="/attackers/:id" element={<AttackerDetail />} />