Add configurable notification TTL (#24829)

* add configurable ttl for active alert notifications

Notifications sent while an alert was active always used a TTL of 0, so the push service dropped them if the device wasn't reachable at that moment and users only received the notification sent when the alert ended. A new `ttl` notifications option, settable globally or per camera, lets the push service retry these notifications for that many seconds. It defaults to 0, and the settings UI warns that a non-zero value can deliver stale notifications.

* make notification ttl a global advanced setting

- Read `ttl` from the global notifications config and hide it on the camera form
- Show it under Advanced Settings on the Notifications page
- Remove extra padding that misaligned the Notifications cards with the rest of the form
- Shorten the ttl warning

* tweaks

* use enum instead of raw seconds value

docs/docs/configuration/advanced/reference.md

@@ -578,6 +578,10 @@ notifications:
   email: "admin@example.com"
   # Optional: Cooldown time for notifications in seconds (default: shown below)
   cooldown: 0
+  # Optional: Delivery of notifications sent while an alert is active (default: shown below)
+  # Options are immediate (deliver right away or drop) and reliable (retry for up to 30 seconds)
+  # NOTE: reliable can deliver late notifications that still link to the live view
+  ttl: immediate
 
 # Optional: Record configuration
 # NOTE: Can be overridden at the camera level

docs/docs/configuration/notifications.md

@@ -43,7 +43,7 @@ Notifications will be prevented if either:
 <ConfigTabs>
 <TabItem value="ui">
 
-1. Navigate to <NavPath path="Settings > Notifications > Notifications" />.
+1. Navigate to <NavPath path="Settings > Notifications" />.
    - Set **Email** to your email address
    - Enable notifications for the desired cameras
 
@@ -108,6 +108,29 @@ Currently, only Chrome supports images in notifications. Safari and Firefox will
 
 Different platforms handle notifications differently, some settings changes may be required to get optimal notification delivery.
 
+### Notification TTL
+
+By default, Frigate sends notifications for an active alert with a `ttl` of `immediate`, so the push service either delivers them immediately or drops them. If your device is briefly unreachable (asleep, switching from Wi-Fi to cellular, or on a weak signal), those notifications are lost and you only receive the notification sent when the alert ends, which is always kept for up to an hour.
+
+Setting `ttl` to `reliable` tells the push service to keep retrying these notifications for up to 30 seconds. This makes delivery more reliable, but a notification delivered late will still say an object is detected, even if the object has already left.
+
+<ConfigTabs>
+<TabItem value="ui">
+
+1. Navigate to <NavPath path="Settings > Notifications" />.
+   - Expand **Advanced Settings** and set **Notification TTL** to **Reliable**
+
+</TabItem>
+<TabItem value="yaml">
+
+```yaml
+notifications:
+  ttl: reliable # retry an undelivered notification for up to 30 seconds
+```
+
+</TabItem>
+</ConfigTabs>
+
 ### Android
 
 Most Android phones have battery optimization settings. To get reliable Notification delivery the browser (Chrome, Firefox) should have battery optimizations disabled. If Frigate is running as a PWA then the Frigate app should have battery optimizations disabled as well.