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 Removed the now-superseded GOTIFY_URL/GOTIFY_TOKEN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/package.json

@@ -16,6 +16,8 @@
     "drizzle-orm": "^0.45.2",
     "express": "^4.21.2",
     "express-session": "^1.18.1",
+    "node-schedule": "^2.1.1",
+    "nodemailer": "^6.9.14",
     "openid-client": "^6.1.7",
     "session-file-store": "^1.5.0",
     "xml2js": "^0.6.2",
@@ -25,6 +27,8 @@
     "@types/express": "^4.17.21",
     "@types/express-session": "^1.18.1",
     "@types/node": "^22.10.5",
+    "@types/node-schedule": "^2.1.7",
+    "@types/nodemailer": "^6.4.17",
     "@types/session-file-store": "^1.2.5",
     "@types/xml2js": "^0.4.14",
     "drizzle-kit": "^0.31.10",