service.rs: Replace per-message Lua+DB seq with simple INCR, only
reconcile DB every 1000 messages (99.9% queries eliminated).
storage.rs: Replace N+1 GET loop with single MGET for both
get_user_sessions and get_workspace_sessions (N+1 → 2 roundtrips).
- session_manager/manager.rs: remove slog::Logger field, update new()
and with_config() to remove log parameter
- email/lib.rs: remove slog::Logger from AppEmail::init()
- rpc/admin/server.rs: remove slog::Logger from serve() and spawn(),
replace with tracing::info!/error!
