Verify diagram screenshots in smoke tests, not just error-free render

Check intermediate .tex/.typ files for \includegraphics and image()
references to mermaid-figure and dot-figure PNGs. This proves Chrome
actually produced screenshot images rather than only checking the
render didn't error.

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

Author: cderv

tests/docs/smoke-all/2026/02/12/dot-pdf.qmd

@@ -1,10 +1,15 @@
 ---
 title: "Graphviz to PDF (#11877)"
-format: pdf
+format:
+  pdf:
+    keep-tex: true
 _quarto:
   tests:
     pdf:
       noErrors: default
+      ensureLatexFileRegexMatches:
+        - ['\\includegraphics.*dot-figure-1\.png']
+        - []
 ---
 
 ## Graphviz Diagram

tests/docs/smoke-all/2026/02/12/mermaid-multi-diagram.qmd

@@ -1,10 +1,15 @@
 ---
 title: "Multiple Mermaid Diagrams to PDF (#11877)"
-format: pdf
+format:
+  pdf:
+    keep-tex: true
 _quarto:
   tests:
     pdf:
       noErrors: default
+      ensureLatexFileRegexMatches:
+        - ['\\includegraphics.*mermaid-figure-1\.png', '\\includegraphics.*mermaid-figure-2\.png', '\\includegraphics.*mermaid-figure-3\.png']
+        - []
 ---
 
 ## Flowchart

tests/docs/smoke-all/2026/02/12/mermaid-pdf-default.qmd

@@ -1,10 +1,15 @@
 ---
 title: "Mermaid to PDF (#11877)"
-format: pdf
+format:
+  pdf:
+    keep-tex: true
 _quarto:
   tests:
     pdf:
       noErrors: default
+      ensureLatexFileRegexMatches:
+        - ['\\includegraphics.*mermaid-figure-1\.png']
+        - []
 ---
 
 ## Mermaid Flowchart

tests/docs/smoke-all/2026/02/12/mermaid-typst.qmd

@@ -1,10 +1,15 @@
 ---
 title: "Mermaid to Typst (#11877)"
-format: typst
+format:
+  typst:
+    keep-typ: true
 _quarto:
   tests:
     typst:
       noErrors: default
+      ensureTypstFileRegexMatches:
+        - ['image\(.*mermaid-figure-1\.png']
+        - []
 ---
 
 ## Mermaid Flowchart