* feat(updates): add CLI release checks and installation guidance

Add optional read-only upstream release checks and keep Diagnostics versions offline. Preserve package-manager ownership and external installation methods. Update usage, README, development notes, translations, changelog and scoped TODO evidence. Refs #268.

* fix(updates): preserve blank paths and align translations

Address Codex Review and CodeRabbit findings. A whitespace-only configured command now reports missing without invoking a PATH executable. Keep French address and Italian CLI gender consistent. Add parser, controller and Diagnostics regressions. Existing docs and the Unreleased feature entry remain accurate.