import_feed_log
Persistent feed activity, accessible to users allowed to use mod_import_feed.
m.import_feed_log.list[FeedId][BeforeId] returns up to 100 events older than the cursor (0 starts at the newest); use
all for all feeds. Invalid filters return an error, never an unfiltered log.
Events retain user, category and content-group IDs as snapshots. History is
removed with its feed or after 30 days. The MQTT topic
model/import_feed/event/log carries committed log IDs. Clients fetch and prepend only the new row.