show validation errors in multi-camera export

Clearing part of a time field in the export time picker set the range to NaN, while the picker kept showing a valid fallback time. The multi-camera Export button then stayed disabled with no explanation, and non-admins could never start an export because a case name was required even though they can't see the case field. The picker now ignores incomplete time values. The multi-camera tab shows inline errors for an invalid range, no selected cameras, and a blank case name, only requires a case name from admins, and prefills a default case name.

web/public/locales/en/components/dialog.json

@@ -67,7 +67,8 @@
       "newCaseDescriptionPlaceholder": "Case description",
       "label": "Case",
       "nonAdminHelp": "A new case will be created for these exports.",
-      "placeholder": "Select a case"
+      "placeholder": "Select a case",
+      "nameRequired": "Case name is required"
     },
     "select": "Select",
     "export": "Export",
@@ -91,9 +92,11 @@
       "selectedCount": "{{selected}} / {{total}} selected",
       "checkingActivity": "Checking camera activity...",
       "noCameras": "No cameras available",
+      "noCamerasSelected": "Select at least one camera",
       "detectionCount_one": "1 tracked object",
       "detectionCount_other": "{{count}} tracked objects",
       "nameLabel": "Export name",
+      "caseNameDefault": "Multi-camera export - {{date}}",
       "namePlaceholder": "Optional base name for these exports",
       "queueingButton": "Queueing Exports...",
       "exportButton_one": "Export 1 Camera",