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.

.gitea/workflows/benchmark.yml

@@ -148,7 +148,7 @@ jobs:
             | while read -r key; do git config --local --unset-all "$key"; done || true
           git config --local lfs.url \
             "https://x-access-token:${LFS_TOKEN}@gitea.tourolle.paris/dtourolle/DarkRoom.git/info/lfs"
-          git lfs pull
+          git lfs pull --exclude="fixtures/**"
 
       - name: Cache cargo
         uses: actions/cache@v4

.gitea/workflows/build-and-test.yml

@@ -96,7 +96,7 @@ jobs:
             | while read -r key; do git config --local --unset-all "$key"; done || true
           git config --local lfs.url \
             "https://x-access-token:${LFS_TOKEN}@gitea.tourolle.paris/dtourolle/DarkRoom.git/info/lfs"
-          git lfs pull
+          git lfs pull --exclude="fixtures/**"
           ls -lR models/
 
       - name: Cache cargo
@@ -213,7 +213,7 @@ jobs:
             | while read -r key; do git config --local --unset-all "$key"; done || true
           git config --local lfs.url \
             "https://x-access-token:${LFS_TOKEN}@gitea.tourolle.paris/dtourolle/DarkRoom.git/info/lfs"
-          git lfs pull
+          git lfs pull --exclude="fixtures/**"
           ls -lR models/
 
       - name: Cache cargo
@@ -406,7 +406,7 @@ jobs:
             | while read -r key; do git config --local --unset-all "$key"; done || true
           git config --local lfs.url \
             "https://x-access-token:${LFS_TOKEN}@gitea.tourolle.paris/dtourolle/DarkRoom.git/info/lfs"
-          git lfs pull
+          git lfs pull --exclude="fixtures/**"
           ls -l models/face models/scene
 
       - name: Cache cargo