Add Servers & Tasks module ported from Schedule Task Manager

Ports cron/systemd task tracking across Debian/Raspbian servers, including
the Linux push agent (install/report/uninstall scripts, rebranded from
"schedule-task-manager-agent" to "homelab-manager-agent") and the
manual-task-entry flow for things an agent can't see (Docker jobs, backups).
The schema (servers/scheduled_tasks tables) was already in place from the
foundation pass, so this is mostly a straight port of the original's
services/routes.

Deliberate change from the original: server/token management (which mints
agent credentials) is now admin-only rather than open to any logged-in user,
and manual task CRUD is gated to operator+ — consistent with how Secrets,
IPAM, and DNS already split "configure credentials" from "everyday edits"
across roles. All mutations are audit-logged.

- server/src/services/tokens.ts, taskSync.ts: ported near-verbatim (agent
  token hashing, the agent-sync-marks-missing-as-stale-not-deleted logic).
- server/src/routes/servers.ts, tasks.ts, agentReport.ts: same contract as
  the original (agent auth is a per-server bearer token, independent of the
  session-based requireAuth used everywhere else).
- web: a single Servers & Tasks page (filter bar, task table grouped by
  server/schedule type, manual task form, and an admin-only server
  management panel with token reveal + copyable install/uninstall commands),
  replacing the original's two separate pages/apps.

Verified: full build passes; a scripted HTTP test against a running server
covers unauthenticated access, role gating at each tier (admin-only server
mgmt, operator+ task mgmt), agent bearer-token auth (valid/invalid/rotated),
manual-vs-agent task edit protection, stale-marking on re-sync, and cascade
delete — 22/22 checks passing. Real agent installation on an actual
Debian/Raspbian host still needs to be tried on the user's network.

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

web/src/utils/date.ts

@@ -0,0 +1,12 @@
+/** Formats a date as "YYYY-MM-DD HH:mm:ss" on a 24-hour clock. */
+export function formatDateTime(date: Date): string {
+  return date.toLocaleString("sv-SE", {
+    year: "numeric",
+    month: "2-digit",
+    day: "2-digit",
+    hour: "2-digit",
+    minute: "2-digit",
+    second: "2-digit",
+    hour12: false,
+  });
+}