Ignore Quarto render artifacts

Single-file `quarto render` emits per-chapter .html and *_files/
directories next to the source (project renders go to _book/). Ignore
both, plus .quarto/ caches, scoped so docs/book/_freeze/ stays tracked.

Author: peterdsharpe

.gitignore

@@ -13,4 +13,11 @@ __pycache__/
 docs/build
 *.vspscript
 .coverage
-.cursor/
+.cursor/
+
+# Quarto render artifacts (book source + _freeze/ are committed; rendered output is not)
+/docs/book/_book/
+/docs/book/*.html
+/docs/book/*_files/
+/docs/book/site_libs/
+.quarto/