Remove generated report artifacts from version control

Add reports/figures/, reports/slides/, reports/tables/ to .gitignore
and untrack previously committed PNGs. These are build artifacts
regenerated by tar_make() and deploy.R.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -27,6 +27,9 @@ _targets.user/data/
 /.quarto/
 **/*.quarto_ipynb
 docs
+reports/figures/
+reports/slides/
+reports/tables/
 
 /dev/
 /scratch/