thermal: alert on recovery (crit→warn, warn→normal)

van-thermal already logged falling crossings to the journal but only paged
Pushover on rising ones. announce() now returns the crossing direction, and a
falling crossing pages an "all-clear" when leaving a level we'd have alerted on,
so the phone that got the rising alert also gets the recovery. thermal-config
gains the pushover_level + shared credentials_path keys. Ignore __pycache__.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

power/thermal-config.json

@@ -3,6 +3,8 @@
   "log_interval": 60,
   "log_path": "/var/log/van-thermal.csv",
   "log_max_bytes": 5242880,
+  "pushover_level": "warn",
+  "credentials_path": "/etc/van-battery/pushover.json",
   "sensors": [
     { "name": "cpu",  "hwmon": "coretemp", "label": "Package id 0", "warn": 80, "crit": 95, "clear_margin": 5 },
     { "name": "nvme", "hwmon": "nvme",     "label": "Composite",    "warn": 65, "crit": 70, "clear_margin": 5 }