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 Removed the now-superseded GOTIFY_URL/GOTIFY_TOKEN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>

server/src/index.ts

@@ -19,9 +19,12 @@ import { serversRouter } from "./routes/servers.js";
 import { tasksRouter } from "./routes/tasks.js";
 import { agentReportRouter } from "./routes/agentReport.js";
 import { integrationsRouter } from "./routes/integrations.js";
+import { settingsRouter } from "./routes/settings.js";
+import { initSecretExpiryScheduler } from "./services/secretExpiryScheduler.js";
 
 warnIfAuthNotConfigured();
 await runMigrations();
+await initSecretExpiryScheduler();
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const webDist = join(__dirname, "..", "..", "web", "dist");
@@ -68,6 +71,7 @@ app.use("/api/servers", serversRouter);
 app.use("/api/tasks", tasksRouter);
 app.use("/api/agent/report", agentReportRouter);
 app.use("/api/integrations", integrationsRouter);
+app.use("/api/settings", settingsRouter);
 
 if (existsSync(webDist)) {
   app.use(express.static(webDist));