refactor(core): extract maxEndTime+serialize to parsers/test-utils.ts (TU) (#1261)

* test(studio): add T5b rotation+motion build-patches characterization

Extends manualEditsDomPatches.test.ts with rotation and motion pairs.
Same 4-pattern structure: populated, empty, clear restores originals,
build/clear symmetry. Merges duplicate manualEditsTypes import block.

* test(studio): add T5c review-fix gaps in manualEditsDomPatches characterization

Fixes four gaps identified in max-setting code review:
- Box-size clear: replace arrayContaining with full ordered toEqual (30 ops)
- Box-size / pathOffset / rotation clear: add empty-string coercion tests
  (origVal||null must produce null, not set property to "")
- Rotation clear: add test for absent STUDIO_ORIGINAL_ROTATION_TRANSFORM_ORIGIN_ATTR
- Motion clear: prove input-independence by calling with both empty and populated
  element and asserting identical output

* refactor(core): extract maxEndTime+serialize to parsers/test-utils.ts (TU)

Deduplicate helpers shared by T1 (htmlParser.roundtrip.test.ts) and T2
(stableIds.test.ts). Both files inline identical implementations; extract
to test-utils.ts so future parser tests (T6a…) import one copy.

Also fix lefthook fallow command to unset GIT_DIR+GIT_INDEX_FILE before
running — those vars are set by git in worktree hook context and block
fallow’s internal temp-worktree creation.

packages/core/src/parsers/stableIds.test.ts

@@ -13,23 +13,7 @@
  */
 import { describe, expect, it } from "vitest";
 import { parseHtml } from "./htmlParser.js";
-import { generateHyperframesHtml } from "../generators/hyperframes.js";
-import type { ParsedHtml } from "./htmlParser.js";
-
-function maxEndTime(elements: ParsedHtml["elements"]): number {
-  if (elements.length === 0) return 0;
-  return Math.max(...elements.map((e) => e.startTime + e.duration));
-}
-
-function serialize(parsed: ParsedHtml): string {
-  return generateHyperframesHtml(parsed.elements, maxEndTime(parsed.elements), {
-    compositionId: "test-comp",
-    resolution: parsed.resolution,
-    styles: parsed.styles ?? undefined,
-    keyframes: parsed.keyframes,
-    stageZoomKeyframes: parsed.stageZoomKeyframes,
-  });
-}
+import { serialize } from "./test-utils.js";
 
 describe("T2 — stable element ids (spec for R1)", () => {
   // --- Spec (red until R1) ---