feat(git-fix-author): 🦉 resolve start from the current branch

[aipal-agent]

Summary

git fix-author can resolve its own start from the checked-out branch.

--current-branch (and GFA_CURRENT_BRANCH) rewrites the unique commits versus the integration line instead of requiring a computed --start. Agents no longer invent that boundary.

Why

Cloud Agents need to repair attribution immediately before push without reconstructing Git surgery.

On a feature branch the unique range is origin/main..HEAD. On the default branch it is only the unpushed commits. An empty unique range, detached HEAD, or a missing integration ref must fail rather than rewrite from the repository root.

Express the Git intent, not the surgery.

Included

• --current-branch as a mutually exclusive alternative to --start / GFA_START;
• integration resolution: origin/HEAD, then origin/main / origin/master, then a local main / master that is not the current branch;
• refusal of detached HEAD, --finish of another branch, an empty unique range, and a missing integration ref;
• GFA_CURRENT_BRANCH=1 for the same mode;
• skill, operation README, and semantics docs that prefer this range; and
• five new integration tests for the happy paths and those refusals.

Usage

git fix-author --current-branch --non-interactive --yes

Identities still come from --name / --email or GFA_*. --yes stays on the command; do not export GFA_YES at boot.

Verification

scripts/validate-skills
  Validated 1 skill(s).

scripts/test
  All 15 tests passed.

The new cases cover a feature unique range versus origin/main, unpushed commits on main, local main as the integration line, GFA_CURRENT_BRANCH, and rejections (in-sync default branch, --start / GFA_START together with current-branch mode, detached HEAD, missing integration).