* feat(providers): persist per-provider source selection

Use the official CLI 0.73.0 set-source writer with version gating and provider-specific CLI validation. Preserve the global request override and retire stale diagnostic results. Update usage, descriptor status, development notes, README, catalogs and changelog; remove completed source-selection work from TODO.

* fix(providers): serialize source writes and roster reloads

* fix(providers): wait for pending descriptor operations