Track creator activity at a glance with new post frequency and activity sparklines

Two new opt-in columns in the Creator and Accounts tabs of Manager — Post activity (14d) and Frequency (14d) — show recent posting trends for every creator and account. Post activity shows a platform-stacked sparkline plus a total posts count; Frequency shows a color-coded badge of average posts per day.

Identity columns in the manager grid now resize more smoothly, and column visibility persists correctly when new columns are added.