Adds cache_limit_bytes column to offline_settings (idempotent ALTER
TABLE) plus get/set methods on the OfflineState store. v2_set_offline_cache_limit
now writes the value to disk in addition to the in-memory cache_state.
At session activation, OfflineCacheState::apply_persisted_limit reads
the stored value and seeds the in-memory limit so the user's chosen cap
survives app restarts. Legacy installs with NULL persisted value keep
the in-memory 5 GB default seeded by init_at.
cc
vicrodh
362f3154ac