Fix selfhost update release source

[Ryson-32]

Summary

• keep fixed-tag installers installing the requested tag while writing the default update source to the stable latest release manifest
• refresh manager runtime env after release metadata updates so compose pull/up uses the new image immediately
• keep dev release installers on the dev update source

Validation

• bash -n public/local/scripts/install.sh public/local/scripts/subboost.sh
• npm --prefix public exec vitest run local/scripts/selfhost-shell.test.ts
• npm exec vitest run service/test/scripts/selfhost-oneclick.test.ts
• npm --prefix public run lint
• npm --prefix public run test:unit

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e3b16235f1

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[chatgpt-codex-connector]

Preserve explicit custom update sources

When an operator installs from a custom/fork/dev manifest by setting SUBBOOST_RELEASE_URL but does not also know to set the newly added SUBBOOST_UPDATE_RELEASE_URL, this persists the default official latest manifest into .env. Since subboost update later reads SUBBOOST_RELEASE_URL in update_cmd, those installs silently switch update channels after the first install instead of continuing to update from the requested source.

Useful? React with 👍 / 👎.