Add backup/update schedule types, copy buttons, cron next-run estimate; update dependencies

- New "backup" and "update" schedule types for manually tracked tasks,
  plumbed through the form, filters, group labels, and API validation.
- Copy buttons next to the agent token and install/uninstall commands
  on the Servers page, so they don't need to be selected by hand.
- Cron jobs now show an estimated "next run" (via cron-parser),
  computed client-side and clearly marked with "~" plus a tooltip,
  since the agent has no way to compute this for cron (unlike systemd
  timers, which report a real value from systemctl).
- Dependency updates: fixes a high-severity SQL injection advisory in
  drizzle-orm (0.38.4 -> 0.45.2, plus drizzle-kit 0.31.10), a qs
  vulnerability pinned past body-parser's own range via an npm
  "overrides" entry, a leftover vulnerable esbuild pulled in
  transitively by drizzle-kit (also via override), and cron-parser
  4 -> 5 (v4 is unmaintained; updated its call site for the new
  CronExpressionParser API). `npm audit` is now clean. Re-verified the
  DB layer end-to-end (migrations, CRUD, agent sync, stale-marking)
  and the cron estimate against the new cron-parser API after the
  upgrade.

package.json

@@ -6,6 +6,10 @@
     "server",
     "web"
   ],
+  "overrides": {
+    "qs": "^6.16.0",
+    "esbuild": "^0.25.0"
+  },
   "scripts": {
     "dev:server": "npm run dev --workspace server",
     "dev:web": "npm run dev --workspace web",