Track incremental Move-to and Canary Settings improvements

[mydmdm]

Purpose

Track small, continuous UI improvements that are independently deliverable and do not necessarily share one implementation boundary. This issue currently contains two concrete requests; each should be investigated, implemented, tested, and reviewed on its own merits.

1. Default “Keep a shortcut in the original Space” to off

The Canvas Move to popover currently initializes the existing source-shortcut option as checked.

Change the default so:

• Keep a shortcut in the original Space remains available in the same location;
• it is unchecked whenever the popover opens;
• an unchecked submission moves the selected content without creating a source Space shortcut;
• checking it preserves the current shortcut-creation behavior;
• closing and reopening the popover resets the choice to unchecked rather than remembering an earlier transient selection.

Preserve the current move semantics, confirmation, error handling, destination navigation, and accessibility.

2. Make the Alpha Canary redeploy branch configurable

The current Settings redeploy surface, shared wire contract, remote check, and runner invocation are fixed to the branch alpha. Allow an owner to configure the branch used by this personal-development deployment, for example x/alpha.

Required direction:

• expose the selected branch near the existing Alpha Canary redeploy setting;
• persist the owner-selected branch through the existing Settings/configuration architecture rather than browser-only state;
• use the configured branch consistently for remote update checks, displayed status, confirmation text, and redeployment;
• retain alpha as the compatibility default when no branch has been configured;
• validate branch names strictly and resolve only the intended origin branch ref; reject invalid, missing, ambiguous, or unavailable refs explicitly;
• keep process execution shell-free with a fixed repository-owned script and bounded arguments—configuration must not enable arbitrary commands, remotes, paths, or extra arguments;
• make the effective branch visible in status and failure messages so users cannot mistake one developer’s Canary branch for another;
• define safe behavior when the configured branch changes while a check or redeployment is already running.

This is still a personal-development Canary helper. It does not add automatic promotion, stable release behavior, rollback, production supervision, or multi-repository deployment.

Acceptance direction

• The Move-to shortcut checkbox defaults to unchecked on every open while remaining user-selectable.
• Tests cover unchecked move, checked shortcut creation, and reopen/reset behavior.
• An owner can configure a valid branch such as x/alpha for Canary checks and redeployment.
• Empty/unconfigured state uses alpha; invalid or unavailable branches fail explicitly without falling back from a configured value.
• Status, confirmation, remote SHA checks, and runner invocation all use and display the same effective branch.
• Branch input cannot alter the remote, executable, repository path, or runner argument shape.
• Existing owner authentication and deployment safety boundaries remain intact.
• Relevant Canvas move and Canary deployment documentation and focused tests are updated.

[mydmdm]

Delivered to the Alpha integration branch by #272 at 929607e0a61691d057e5ef5f6729510a4d3ad8a0. Both approved UI improvements are present in the current alpha history. Further Canary regressions can reopen this issue or be tracked through a focused follow-up.