Add the twelve-frame 6D panorama set as an LFS fixture

fixtures/pano/2025-08-05: _MG_8320 … 8331, one portrait hand-held sweep
at 50 mm with a stop of shutter drift and sky in every frame — the set
§3.11 is built against, with each of those facts named as the test it
is. fixtures/** is tracked in LFS like the models but with the opposite
default: CI's pulls exclude it, so a build never fetches 325 MB it does
not use.

.gitattributes

@@ -10,3 +10,13 @@
 # detects exactly that and fails with an instruction rather than embedding the
 # pointer and failing at inference time.
 *.onnx filter=lfs diff=lfs merge=lfs -text
+
+# Test photographs live in LFS too, and are fetched only by the tests that
+# need them.
+#
+# `fixtures/**` holds real camera files — a twelve-frame panorama set is
+# 325 MB — and CI's `git lfs pull` excludes the directory, so a checkout
+# carries pointers there until a merge test asks for the frames. Same
+# reasoning as the models, with the opposite default: the model is not
+# optional and the fixtures are.
+fixtures/** filter=lfs diff=lfs merge=lfs -text