feat(updates): opt in to test versions (alpha/beta) from Settings

[lippdev]

Summary

• Settings → Receive test versions (alpha and beta), off by default, in both the desktop and the console interface.
• Update rule (UpdateChannel, unit-tested): pre-releases are offered when the user opted in or a pre-release is already installed. Turning it off never downgrades; a test build moves to the next stable one when it ships.
• Turning it on shows a warning in the status bar. Strings in pt-BR, en-US and es-ES.

The same change goes to a 1.5.1 built from v1.5.0, so stable users can opt into the 1.6 tests.

🤖 Generated with Claude Code

[pullfrog]

ℹ️ Minor changelog convention suggestion inline.

Reviewed changes This review covers the opt-in prerelease update flow, its settings UI and persistence, localization, and tests.

• Update channel Stable builds can see prereleases when opted in; prerelease builds continue receiving prereleases.
• Settings Adds the saved option to desktop and console settings, with a warning when enabled.
• Localization and tests Adds the strings in all three catalogs and tests the channel-selection rule.

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Note: 1 inline comment(s) dropped because they did not anchor to lines inside the PR diff:

• CHANGELOG.en-US.md:30 (RIGHT) — line 30 (RIGHT) is not inside a diff hunk

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[pullfrog]

One minor changelog convention note: please add (#103) to both new Unreleased bullets in CHANGELOG.en-US.md and CHANGELOG.md. The submitted review could not anchor this inline because the changelog line was outside the detected diff hunk.

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[pullfrog]

✅ No new issues found.

Reviewed changes This review covers the newly added 1.5.1 release notes in both changelog languages.

• 1.5.1 changelog Added notes explaining that 1.5.1 users can opt into 1.6 test versions from Settings.

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