Implement fast-forward Pull, normal Push, and Publish Branch

[Traviinam]

Summary

• add fast-forward-only Pull for the exact configured Upstream
• add normal Push to the exact Upstream and confirmed same-name Publish
• use authoritative branch merge metadata for custom refspec mappings
• serialize Remote Operations and reconcile exact Remote-tracking state without force
• preserve truthful Succeeded, Partial Success, Failed Known, and Unknown Outcome classifications
• provide divergence guidance targeting the exact selected Worktree Terminal

Verification

• focused tests: 29 passed
• full test suite: 278 passed
• TypeScript typecheck
• ESLint
• Prettier
• production build
• git diff check

Closes #14