chore: remove issue screenshots from the source tree (#1259)

Two PR screenshots landed at the repo root in #1241 and have been shipping as
part of the source tree since. Nothing references them.

Screenshots belong on a `screenshots/*` branch — that is what those branches
are for, and how every other UI change here has attached its evidence. Added
ignore rules so the next one cannot follow the same path, anchored with a
leading slash so docs/ keeps its own five images and test-assets/ keeps the
fixtures the e2e specs load.

Verified no other tracked file matches the new patterns.

Co-authored-by: Paul Nothaft <paul@MacStudio-von-Paul.local>

.gitignore

@@ -145,3 +145,16 @@ ml/venv/
 # SHA-256 at build time; a 90MB blob must not end up in git history.
 ml/*.onnx
 ml/*.h5
+
+# Issue / PR screenshots belong on a `screenshots/*` branch, never on main or
+# stable — that is what those branches exist for. Two landed at the repo root
+# in #1241 and shipped as part of the source tree.
+#
+# Anchored with a leading slash so docs/ keeps its own images.
+/issue-*.png
+/issue-*.jpg
+/screenshot-*.png
+/screenshot-*.jpg
+/*-screenshot.png
+/*-screenshot.jpg
+