Add flag to disable standard 'just release' when custom release command exists

[chicks-net]

Problem

The template provides a standard just release <version> command that creates GitHub releases with auto-generated notes. However, some projects using this template have their own custom release mechanisms that are more appropriate for their specific needs.

Example: macaw has its own release command that's better suited to that project's workflow.

Currently, there's no clean way to disable or override the standard just release command without modifying the imported .just/gh-process.just module, which makes updates harder.

Proposed solution

Add a flag to .repo.toml to disable the standard release command:

[flags]
standard-release = false

When standard-release = false:

• The just release recipe could either be hidden or display a message pointing to the project's custom release command
• The just release_age recipe might also need similar treatment

Benefits

• Projects can cleanly opt out of the standard release workflow
• Template updates remain easy (no need to modify imported modules)
• Clear separation between template defaults and project-specific customizations
• Follows existing pattern of using .repo.toml flags for feature toggles

Implementation notes

• The cue-verify recipe should validate this flag
• Consider whether to hide the recipe entirely or show a helpful message
• May need to coordinate with custom release commands in .just/pr-hook.just or a new module like .just/release-hook.just