fix(config): Refresh stored target metadata

[reneleonhardt]

🧢 Changes

• Add but config target --refresh to update the stored target commit from the
  already configured remote-tracking ref.
• Keep but config target --push-remote <remote> working without a positional
  target branch.
• Preserve target identity, refs, workspace, branch tips, index, and worktree.
• Reject refresh while named or anonymous stacks are applied, and reject a
  simultaneous target change.
• Normalize fully qualified remote-ref input.

☕️ Reasoning

Fetching can advance the configured remote-tracking ref while the project keeps
an older stored target commit. Re-selecting the same target intentionally
preserves that commit, leaving no supported metadata-only repair.

An explicit refresh provides a bounded recovery path without pulling, moving a
protected local default branch, or disturbing workspace state. This is useful
for human and agentic coding workflows that separate remote refresh from
workspace integration.

🧪 Reproduction

but pull --check
but config target --refresh

Before this fix, the first command could advance the configured tracking ref
while the stored target commit remained stale. Re-selecting the same target was
intentionally a no-op.

✅ Verification

• Focused workspace, parser, CLI, and push-remote compatibility tests passed.
• The tests cover idempotence, applied-stack rejection, and preservation of
  refs, HEAD, workspace, index, worktree, target name, and push remote.
• Formatting, warnings-denied Clippy with --no-default-features, focused diff
  review, and commit-signature verification passed.

Developed with carefully directed, manually reviewed AI assistance.

Co-Authored-By: GPT-5.6 Sol codex@openai.com

[Byron]

Thanks for tackling this.

However, I think it's best to close it and wait for a couple of other fixes to land that might affect it positively.