feat(config): add configurable default shutdown delay for shutdown actions

readme.md

@@ -219,12 +219,16 @@ nupst uninstall               # Completely remove NUPST (requires root)
 
 NUPST stores configuration at `/etc/nupst/config.json`. The easiest way to configure is through the interactive CLI commands, but you can also edit the JSON directly.
 
+`defaultShutdownDelay` sets the inherited delay in minutes for shutdown actions that do not define
+their own `shutdownDelay`.
+
 ### Example Configuration
 
 ```json
 {
   "version": "4.3",
   "checkInterval": 30000,
+  "defaultShutdownDelay": 5,
   "httpServer": {
     "enabled": true,
     "port": 8080,
@@ -395,7 +399,7 @@ Actions define automated responses to UPS conditions. They run **sequentially in
 
 | Field           | Description                        | Default |
 | --------------- | ---------------------------------- | ------- |
-| `shutdownDelay` | Minutes to wait before shutdown     | `5`     |
+| `shutdownDelay` | Minutes to wait before shutdown     | Inherits `defaultShutdownDelay` (`5`) |
 
 #### Webhook Action
 
@@ -610,16 +614,16 @@ UPS Devices (2):
     Host: 192.168.1.100:161 (SNMP)
     Groups: Data Center
     Action: proxmox (onlyThresholds: battery<30%, runtime<15min)
-    Action: shutdown (onlyThresholds: battery<20%, runtime<10min, delay=10s)
+    Action: shutdown (onlyThresholds: battery<20%, runtime<10min, delay=10min)
 
   ✓ Local USB UPS (online - 95%, 2400min)
     Host: 127.0.0.1:3493 (UPSD)
-    Action: shutdown (onlyThresholds: battery<15%, runtime<5min, delay=5s)
+    Action: shutdown (onlyThresholds: battery<15%, runtime<5min, delay=5min)
 
 Groups (1):
   ℹ Data Center (redundant)
     UPS Devices (1): Main Server UPS
-    Action: shutdown (onlyThresholds: battery<10%, runtime<5min, delay=15s)
+    Action: shutdown (onlyThresholds: battery<10%, runtime<5min, delay=15min)
 ```
 
 ### Live Logs