* fix(settings): reject provider rosters from failed CLI processes

Forward the executable DataSource exit code into the pure roster response parser. Valid provider JSON from a failed command previously populated Popup and Panel settings without an error. Keep structured and redacted error messages and reject selectable identities on failure.

Add direct QtTests and real-process regression coverage. Update Unreleased, usage and development guides, and regenerate the translation template. TODO remains unchanged because this fixes existing settings behavior without delivering a parity feature or adding CLI contracts.

* fix(settings): preserve CLI errors with malformed roster output

A failed roster process could emit partial JSON or a banner. The JSON parse catch returned before considering its exit status, hiding useful stderr or the exit-code message. Prefer the failed-process outcome in that catch while keeping parser errors for successful processes and structured CLI errors for valid JSON.

Extend real-process and pure Qt regressions and document the error precedence. Existing Unreleased and usage-guide entries already describe this behavior; no translation, configuration, metadata, or TODO changes are needed.