test: migrate 207 test files to typed fixture registry (phase 5)

Codemod rewrites all five ad-hoc fixture-path styles to import from the
typed registry (tests/fixtures/index.ts):
- join(__dirname, "..", "fixtures", ...) inline patterns (100 files)
- const FIXTURES = join(__dirname, ...) + join(FIXTURES, ...) (92 files)
- process.cwd()-based paths (10 files)
- path.resolve(__dirname, ...) patterns (5 files)

Registry extended with 8 new keys (portraitJpg, portraitHeic,
motorcycle, svgLogo, barcodeAvif, qrAvif, crossFormatChat,
multipageTiff) and directory accessors (fixtureDir, fixtureRoot).

Dynamic directory scanners (format-matrix-generated,
format-matrix-multimodal, hostile-inputs) preserved via fixtureDir
imports. No fixtures swapped, bytes identical.

Parity gate: dropped 0, net-new 388.

tests/unit/image-engine/edit-metadata.test.ts

@@ -1,4 +1,3 @@
-import { readFileSync } from "node:fs";
 import { createRequire } from "node:module";
 import path from "node:path";
 import { beforeAll, describe, expect, it } from "vitest";
@@ -12,15 +11,14 @@ const exifReader = require(
 ) as typeof import("exif-reader").default;
 
 import { editMetadata } from "@snapotter/image-engine";
-
-const FIXTURES_DIR = path.resolve(__dirname, "../../fixtures");
+import { fixtures, readFixture } from "../../fixtures/index.js";
 
 let jpgWithExif: Buffer;
 let png200x150: Buffer;
 
 beforeAll(() => {
-  jpgWithExif = readFileSync(path.join(FIXTURES_DIR, "test-with-exif.jpg"));
-  png200x150 = readFileSync(path.join(FIXTURES_DIR, "test-200x150.png"));
+  jpgWithExif = readFixture(fixtures.image.exifGps);
+  png200x150 = readFixture(fixtures.image.base.png200);
 });
 
 async function getExif(img: sharp.Sharp) {