feat: Add cameras[].media.severities to filter review media by severity

Review queries were issued without a severity filter, so the thumbnail
bar, gallery and timeline showed every Frigate review item -- alerts and
detections alike -- regardless of what a camera is configured to alert
on. Severity could only be narrowed interactively, in the media filter
drawer, and that choice did not persist.

`media.severities` resolves into the default query the same way
`media.reviewed` does, and is overridden by an explicit severity filter
so the media filter drawer keeps working. Unset means all severities, so
existing behaviour is unchanged.

    cameras:
      - camera_entity: camera.office
        media:
          severities:
            - high

src/components-lib/editor/schema/cameras.ts

@@ -432,6 +432,18 @@ export const getCameraSchema = (options: CameraSchemaOptions): HAFormSchema[] =>
             { value: 'all', label: localize('config.cameras.media.revieweds.all') },
           ]),
         },
+        {
+          name: 'severities',
+          label: localize('config.cameras.media.severities'),
+          selector: createSelectSelector(
+            [
+              { value: 'high', label: localize('common.severities.high') },
+              { value: 'medium', label: localize('common.severities.medium') },
+              { value: 'low', label: localize('common.severities.low') },
+            ],
+            { multiple: true },
+          ),
+        },
         {
           name: 'folders',
           selector: createSelectSelector(options.folders, { multiple: true }),