1. Prevent user_id impersonation in contact submissions
- Remove user_id from submission_changeset cast fields
- Pass user_id as a separate server-side argument to create_contact/2
- Client form params can no longer forge account-linked contacts
2. Restrict flag toggle to admins only
- Add admin? guard to toggle_flag event handler
- Hide flag button from non-admin users in template
3. Reset enrichment on timestamp edits
- Add qso_timestamp to the fields that trigger enrichment reset
- Prevents stale weather/HRRR/IEMRE data after time changes