Select which files to include in a personal build

### Area

VCS Operations (remote run, changes)

### Problem or use case

Personal builds need a way to include selected local changes while leaving unrelated work out of the uploaded patch.

### Proposed solution

Add explicit file selection to the Git-generated `--local-changes` flow. Settle the repeatable flag syntax before implementation; paths containing spaces or commas must be representable.

Preserve the current default and its upstream merge-base semantics. Limit both tracked and untracked changes to the selected paths, accounting for deletions and renames. Report invalid selections or an empty resulting patch clearly, and define behavior when a supplied patch file/stdin is used instead of Git.

Verify the patch contents with tracked, untracked, deleted, renamed, and excluded files, then run a Sandbox personal build to confirm the selected changes arrive. Glob/regex matching and a redundant `--all` flag are outside the first slice.

### Alternatives considered

Generate a scoped patch and supply it through the existing patch-file/stdin support. This already works but requires callers to manage patch generation.

### Contribution

- [ ] I'd be willing to submit a PR (once it's `status:finalized`)