Restructure documentation, validate metadata removal, consolidate assets

tests/conftest.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from pathlib import Path
+from typing import TYPE_CHECKING
 
 import cv2
 import numpy as np
@@ -10,21 +10,20 @@ import pytest
 from PIL import Image
 from PIL.PngImagePlugin import PngInfo
 
-CORPUS_NEG_DIR = Path(__file__).resolve().parent.parent / "data" / "synthid_corpus" / "images" / "neg"
+if TYPE_CHECKING:
+    from pathlib import Path
 
 
 @pytest.fixture
-def clean_photo() -> Path:
-    """A verified-negative real photo from the corpus neg/ set.
+def clean_photo(tmp_path: Path) -> Path:
+    """Create a deterministic image with no provenance metadata.
 
-    Used by the "non-AI image" assertions (no SynthID, verdict unknown). These
-    are real photos with no AI provenance, the ground truth for "must not false-
-    positive". Skips if the corpus is not checked out.
+    The assertions using this fixture exercise metadata and provenance behavior,
+    so a generated fixture is sufficient and avoids committing personal photos.
     """
-    files = sorted(CORPUS_NEG_DIR.glob("*")) if CORPUS_NEG_DIR.exists() else []
-    if not files:
-        pytest.skip("no corpus neg/ images present")
-    return files[0]
+    path = tmp_path / "clean-control.png"
+    Image.new("RGB", (128, 96), color=(90, 140, 190)).save(path)
+    return path
 
 
 @pytest.fixture