Remove stray PR screenshots accidentally committed under docs/ (#1351)

PRs #738 and #644 committed their before/after review screenshots into the
repo (docs/a11y/focus-*.png, docs/a11y/login-*.png, docs/gallery-314-*.png).
Nothing references these files, so they only showed up as "random images" in
the doc folder (issue #1335). The README hero image and the feature preview
clips are referenced and are left untouched.

Add tests/test_docs_no_orphan_images.py to guard against recurrence: it fails
if any image under docs/ is referenced by no tracked text file.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_docs_no_orphan_images.py

@@ -0,0 +1,64 @@
+"""Regression guard for issue #1335 — PR review screenshots were committed into
+docs/ (docs/a11y/*.png from #738, docs/gallery-314-*.png from #644) where they
+served no purpose: nothing in the repo referenced them, so they just showed up
+as "random images" in the doc folder.
+
+This test fails if any image under docs/ is orphaned — present in the tree but
+referenced by no tracked text file. The intended doc assets (the README hero
+image and the feature preview clips) are referenced, so they pass; a stray
+screenshot dropped in by a future PR would not.
+"""
+import subprocess
+from pathlib import Path
+
+import pytest
+
+REPO = Path(__file__).resolve().parent.parent
+IMAGE_EXTS = {".png", ".jpg", ".jpeg", ".gif", ".webp", ".bmp"}
+# Files a referenced image name could legitimately appear in.
+TEXT_EXTS = {".md", ".html", ".htm", ".js", ".ts", ".css", ".py", ".sh",
+             ".json", ".yml", ".yaml", ".txt"}
+
+
+def _tracked(paths_under):
+    """Git-tracked files under a path, or None if git isn't available."""
+    try:
+        out = subprocess.run(
+            ["git", "ls-files", paths_under],
+            cwd=REPO, capture_output=True, text=True, timeout=30,
+        )
+    except (OSError, subprocess.SubprocessError):
+        return None
+    if out.returncode != 0:
+        return None
+    return [REPO / line for line in out.stdout.splitlines() if line.strip()]
+
+
+def test_no_orphan_images_in_docs():
+    docs_images = _tracked("docs")
+    if docs_images is None:
+        pytest.skip("not a git checkout")
+    docs_images = [p for p in docs_images if p.suffix.lower() in IMAGE_EXTS]
+    assert docs_images, "expected docs/ to still contain referenced doc assets"
+
+    # All tracked text we might reference an image from.
+    all_tracked = _tracked(".") or []
+    haystack = []
+    for p in all_tracked:
+        if p.suffix.lower() not in TEXT_EXTS:
+            continue
+        try:
+            haystack.append(p.read_text(encoding="utf-8", errors="ignore"))
+        except OSError:
+            continue
+    blob = "\n".join(haystack)
+
+    orphans = [
+        str(img.relative_to(REPO))
+        for img in docs_images
+        if img.name not in blob
+    ]
+    assert not orphans, (
+        "unreferenced image(s) committed under docs/ — likely PR screenshots "
+        f"added by accident (see #1335): {orphans}"
+    )