docs: ask for pictures in issues and pull requests

The bug template's Evidence asks for a screenshot or recording first,
marked up, and a section for meshes; the feature template gains a
Pictures field; the pull request template and CONTRIBUTING ask for
before/after pictures of any visible change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

.github/pull_request_template.md

@@ -2,10 +2,14 @@ Closes #
 
 ## What and why
 
+## Before and after
+<!-- For any visible change (the view, meshes, panels, results, icons): a picture before and after. Drag them in here. -->
+
 ## How it was verified
 <!-- Tests added or changed; oracle cases (tests/oracle) for solver and meshing results, with their cited references. -->
 
 ## Checklist
 - [ ] The issue was assigned to me before I started (see CONTRIBUTING.md)
 - [ ] `cargo fmt --all`, `cargo clippy -p <crates I touched> --all-targets -- -D warnings` and their tests pass
+- [ ] Before/after pictures for any visible change
 - [ ] No code, text or data from GPL-family projects or commercial CAE products