Add UPS email notifications and automatic UPS shutdown

- Add email notifications via PVE::Notify for all UPS events:
  - ONBATT: when UPS switches to battery
  - ONLINE: when power is restored
  - LOWBATT: critical battery level
  - SHUTDOWN_START/NODE/PRIMARY: during cluster shutdown
  - COMMBAD: communication lost with UPS

- Add automatic UPS shutdown command after cluster shutdown
  (protects against power surge when power returns)

- Update upssched.conf with ONLINE handler and immediate ONBATT notification

- Add notification templates for HTML and text emails

- Update documentation with new features and timer configuration

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

proxmox/ups/config/notification-templates/ups-power-event-body.txt.hbs

@@ -0,0 +1,31 @@
+========================================
+UPS POWER EVENT - {{ event_title }}
+========================================
+
+Hostname: {{ hostname }}
+Date: {{ event_date }}
+Event: {{ event_type }}
+
+{{ event_description }}
+
+UPS STATUS:
+-----------
+Status: {{ ups_status }}
+Battery Charge: {{ battery_charge }}%
+Input Voltage: {{ input_voltage }}V
+{{#if battery_runtime}}
+Battery Runtime: {{ battery_runtime }} min
+{{/if}}
+
+{{#if action_taken}}
+ACTION: {{ action_taken }}
+{{/if}}
+
+{{#if next_steps}}
+NEXT STEPS: {{ next_steps }}
+{{/if}}
+
+========================================
+Log: /var/log/ups-events.log
+Script: /usr/local/bin/upssched-cmd
+========================================