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/e2e/document-mode.spec.ts

@@ -1,7 +1,14 @@
 import path from "node:path";
 import { expect, test, waitForProcessing } from "./helpers";
 
-const PDF_FIXTURE = path.join(process.cwd(), "tests", "fixtures", "test-3page.pdf");
+const PDF_FIXTURE = path.join(
+  process.cwd(),
+  "tests",
+  "fixtures",
+  "document",
+  "valid",
+  "test-3page.pdf",
+);
 
 test.describe("Document display mode (rotate-pdf)", () => {
   test("uploads a PDF, rotates it, and shows the document canvas with processed result", async ({