Uptime: heartbeat (push) monitors show an empty Advanced tab and a useless response-time chart

Imported from GitHub issue El-SaMa/oma#219 by @El-SaMa.

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Found in a click-through of /apps/uptime on 2026-10-15 (monitor "ops: disk space").

• Edit modal: the Advanced tab renders nothing for push monitors (only Cancel / Save). Hide the tab for push, or show one line saying heartbeats have no advanced options.
• Detail modal: "Response time, last 24 hours" shows "Not enough checks yet" and "Avg — · min — · max —". Push beats have no latency, so hide the chart for push.
• Card footer shows "Heartbeat (push) — #ops" because latency is null.

Files: apps/web/components/uptime/uptime-monitor-form.tsx, uptime-monitor-detail.tsx, uptime-monitor-board.tsx. Check: https://oma.lanetti.fi/apps/uptime (open a push monitor, Edit, Advanced).