miscellaneous fixes

- keep base path in recording share links
- reject non-positive scale on recordings/unavailable, which looped forever on the event loop
- reject negative vod event padding, which cleared has_clip
- clamp negative preview gif/mp4 offsets
- don't delete exports that are still in progress
- hash on unknown login usernames so timing doesn't reveal valid users
- include the first minute of the events time-of-day filter
- show an error when the push subscription is refused
- don't wipe an unnamed known plates entry when Add is pressed again
- use elapsed hours for export last N hours so DST doesn't shift the range

docs/static/frigate-api.yaml

@@ -6371,6 +6371,7 @@ paths:
           required: false
           schema:
             type: integer
+            minimum: 0
             description: Padding to apply to the vod.
             default: 0
             title: Padding
@@ -7576,6 +7577,7 @@ paths:
           required: false
           schema:
             type: integer
+            minimum: 1
             default: 30
             title: Scale
       responses: