sol: add auto_updates

[coyaSONG]

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After making any changes to a cask, existing or new, verify:

• The submission is for a stable version or documented exception.
• brew audit --cask --online <cask> is error-free.
• brew style --fix <cask> reports no offenses.

Additionally, if adding a new cask:

• Named the cask according to the token reference.
• Checked the cask was not already refused (add your cask's name to the end of the search field).
• brew audit --cask --new <cask> worked successfully.
• HOMEBREW_NO_INSTALL_FROM_API=1 brew install --cask <cask> worked successfully.
• brew uninstall --cask <cask> worked successfully.

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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes, including zap stanza paths.

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Related to #170994.

Marks Sol as self-updating. Its source starts SPUStandardUpdaterController with the app, and the installed app bundles Sparkle 2.9.3 with the same SUFeedURL used by the cask plus a SUPublicEDKey. Livecheck confirmed current/latest version 2.1.346.

AI assistance: OpenAI Codex was used for policy and upstream source review and to prepare this one-line change. I ran cask audit, style, and livecheck; installed the cask; inspected the installed version, primary and login-helper bundle identifiers, Sparkle framework, feed URL, and public update key; and uninstalled it. The existing zap paths were reviewed against com.ospfranco.sol, com.ospfranco.sol-LaunchAtLoginHelper, and the corresponding support, HTTP storage, and preference locations.

Additional upstream-artifact observation: the official 2.1.346 asset matched its published SHA-256 and installed successfully, but codesign --verify --strict reports the original app bundle signature as modified for both arm64 and x86_64. This metadata-only PR does not alter that asset.