test: reorganize fixture files into modality-first layout (phase 6b)

Move all fixture files from flat/mixed dirs (content/, media/, documents/,
formats/, hostile/, root loose) into the modality-first hierarchy:
image/{valid,formats,edge,hostile}, video/{valid,formats,hostile},
audio/{valid,formats,hostile}, document/{valid,formats,edge,hostile},
data/valid/, security/. Update index.ts paths, fixtureDir aliases,
all literal refs in 17 e2e/qa/script files, manifest.json, and the
three generator scripts. 163 files moved, 0 dropped, 100 new tests
from expanded document scan.

tests/integration/platform/ownership-enforcement.test.ts

@@ -36,7 +36,7 @@ let userAPipelineId: string;
 
 // Load test fixture
 const fixtureBuffer = readFileSync(
-  join(import.meta.dirname, "..", "..", "fixtures", "test-1x1.png"),
+  join(import.meta.dirname, "..", "..", "fixtures", "image", "edge", "test-1x1.png"),
 );
 
 /** Register a user, clear mustChangePassword, log in, return token. */