fix: remove root version marker dependency from offline update flow

[lixfrank]

Issue for this PR

Closes #269

Type of change

• Bug fix
• Refactor / code improvement
• New feature
• Documentation

What does this PR do?

This removes the offline installer/update flow's dependency on the root .aether_web_version marker.

Instead of reading the root marker to decide which version is installed or active, the scripts now resolve versions from the installed package directories themselves. For darwin and linux, the update launchers, installer checks, and version pruning logic now derive versions from each aether_<version> directory and its package-local marker. For windows, the installer and updater now do the same when checking installed versions, active versions, and retained versions.

The root .aether_web_version file is no longer written as part of the update flow. Existing stale copies are removed during install/update so version selection depends only on the package directories, which are the actual source of truth.

How did you verify your code works?

• Ran bash -n Update/update_darwin.command
• Ran bash -n Update/aether_darwin_installer.command
• Ran bash -n Update/aether_darwin_installer_devtest.command
• Ran bash -n Update/update_linux.sh
• Ran bash -n Update/aether_linux_installer.sh
• Ran bash -n Update/aether_linux_installer_devtest.sh
• Ran a local mock darwin update flow and confirmed a deliberately wrong root .aether_web_version value did not affect the installed or launched version
• Reviewed the corresponding windows installer/update logic changes for root marker removal

Screenshots / recordings

Not applicable.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[code-JDS]

/oc review

[github-actions]

This PR removes the root .aether_web_version marker dependency from the offline installer/update flow, shifting version resolution to per-directory markers and directory-name parsing. The approach is sound and consistent across platforms, but there is one bug.

• Bug — update_windows.bat :active_dir fallback loop uses stale $env:DIR (medium severity). In the for /d %%i fallback block inside :active_dir, the inner PowerShell command references $env:DIR, but DIR is never set to %%i within the loop. It will either be empty or carry a stale value from a prior :installed call. This means the fallback cannot correctly resolve versions from directories lacking a per-directory .aether_web_version marker. A set "DIR=%%~fi" needs to be added before the inner for /f, and since the loop body is parenthesized, delayed expansion (set "DIR=%%~fi" before the for /f, or restructure to avoid the scoping issue) will be required to propagate it into the PowerShell invocation.

[code-JDS]

请复核opencode review提出的问题是否确实存在

This PR has been corrected.