power: add van-nvme-watch — pages on NVMe I/O-timeout/reset recurrence

Tails journalctl -kf for the "nvme nvmeN: I/O tag ... timeout, reset
controller" signature that crashed and corrupted the root fs on 2026-08-02
(and recurred 2026-08-04, that time self-healing). Watches a short grace
window to tell a clean self-heal from an escalation (repeated timeout or a
following ext4 error) before paging via the existing Pushover credentials,
with a live SMART/superblock snapshot in the alert body.

power/nvme-watch-config.json

@@ -0,0 +1,7 @@
+{
+  "nvme_device": "nvme0",
+  "fs_device": "/dev/nvme0n1p2",
+  "grace_period": 20,
+  "cooldown": 300,
+  "credentials_path": "/etc/van-battery/pushover.json"
+}