Add accessibility before/after screenshots (#86)

Illustration assets for the PR: login submit-button contrast and the
sidebar keyboard focus ring, before vs after. Whitelist docs/ subfolder
images in .gitignore so curated screenshots are tracked.

.gitignore

@@ -66,6 +66,11 @@ output.txt.txt
 !docs/*.png
 !docs/*.gif
 !docs/*.webp
+# …and curated docs/ subfolder assets (e.g. accessibility before/after shots).
+!docs/**/*.png
+!docs/**/*.jpg
+!docs/**/*.gif
+!docs/**/*.webp
 
 # Reports and temp files
 reports/