scrape_schedules had no interval column -> every source ran daily. Add
interval_days from default_params (default 1, backward-compatible) so
compute_next_run_at can schedule N days ahead. Set avito_full_load_exhaustive
to interval_days=7 (weekly full pass for last_seen/delisting + silent price
edits); avito_full_load stays daily incremental.
run_avito_full_load gains incremental_days param -> passes since= to the
(merged) incremental SERP engine. avito_full_load schedule flipped to
incremental_days=2 (shallow, date early-stop -> avoids deep-pagination 429
bans). New avito_full_load_exhaustive source runs the full walk weekly to
refresh last_seen (10-day delisting TTL) and catch silent price edits.
