Fix CV update workflow: git rebase failing on dirty working tree

[Copilot]

git pull --rebase was running before git add, so every run failed instantly — Git refuses to rebase over unstaged changes left by the R script and Typst compiler.

Changes

• Reorder git operations: git add + git commit now happen before any git pull --rebase; the retry loop's rebase only runs after the tree is clean
• Drop pre-commit pull: the git pull --rebase before staging was removed entirely — divergence is already handled by the push-retry loop
• Fix no-change detection: git diff --quiet silently ignores untracked files; added git ls-files --others check to catch a brand-new cv/resume.pdf

# Before (broken)
git pull --rebase origin main        # ← exits 128: unstaged changes from R/Typst
git add cv/resume.pdf cv/resume.typ research/index.qmd
git commit -m "Automated CV update [skip ci]"

# After
git add cv/resume.pdf cv/resume.typ research/index.qmd
git commit -m "Automated CV update [skip ci]"
# push retry loop calls git pull --rebase here, when tree is clean ✓