- Fix frontend Logs.vue to use correct field names (entity_type, entity_name, old_value, new_value)
- Add user and source_ip columns to logs table
- Add details column showing old_value -> new_value transitions
- Fix backend logs API to support pagination (page, page_size, search)
- Add search support across all log fields (action, entity_type, entity_name, username, values)
- Return proper {list, total, page, page_size} response format
