Build the Settings module: notification channels, event toggles, DNS badge colors

The Settings page was a "coming soon" placeholder. Port Sloth Manager's
settings feature set: Gotify/ntfy/SMTP/webhook notification channels
(each with its own test-send button), per-event toggles (DNS record
added/updated/deleted, a daily secret-expiry digest with configurable
time/timezone), and per-provider DNS badge color customization.

Settings persist in the existing `settings` key/value table via a new
settingsStore service; a notify service fans a message out to every
enabled channel. DNS record add/update/delete now fire notifications,
and a node-schedule job re-arms itself whenever the notification
settings change. Removed the now-superseded GOTIFY_URL/GOTIFY_TOKEN
env vars in favor of in-app configuration.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/App.tsx

@@ -10,7 +10,7 @@ import Ipam from "./pages/Ipam";
 import Dns from "./pages/Dns";
 import ServersTasks from "./pages/ServersTasks";
 import Integrations from "./pages/Integrations";
-import ComingSoon from "./pages/ComingSoon";
+import Settings from "./pages/Settings";
 import AppShell from "./layout/AppShell";
 
 const roleRank: Record<UserRole, number> = { viewer: 0, operator: 1, admin: 2 };
@@ -84,7 +84,7 @@ export default function App() {
           path="/settings"
           element={
             <RequireRole user={user} minRole="admin">
-              <ComingSoon title="Settings" />
+              <Settings />
             </RequireRole>
           }
         />