Patch Manifold v3.5.2: fix a heap overflow in CsgLeafNode::Compose

[revarbat]

Bug. Manifold v3.5.2 reads past the end of a heap array in CsgLeafNode::Compose:

• Compose calls combined.RemoveDegenerates() and then sorts the mesh (SortGeometry → GatherFaces/ReindexFace).
• On some inputs, the cleanup leaves the face data inconsistent, and the sort then reads 96 bytes past a 663 KB array.
• MinkowskiDifference.ShrinksANonConvexBodyOnEverySide reaches it, a holed plate eroded by a sphere. It fails under AddressSanitizer on main. A normal build doesn't notice, which is why CI never has.

Isolated and bisected upstream:

• A standalone program using only Manifold reproduces it: the evaluator's exact plate and sphere meshes, then plate.MinkowskiDifference(sphere).
• Bisected across the 77 master commits since v3.5.2's branch point. It's fixed by Improved decimation elalish/manifold#1789 "Improved decimation" (969b1417), which deletes that same RemoveDegenerates() call. The rest of #1789 is a new decimator.
• v3.5.2 with only that call removed runs the repro clean, with the same result as master.
• #1789 isn't in any release: 3.5.3 and 3.5.4 change only the release pipeline and WASM. Moving to master isn't an option either. It removes CrossSection::FillRule, which we use in 8 places, and it has a separate regression: eroding a cube by a sphere returns an empty result.

Change. FetchContent now runs cmake/patch_manifold.cmake as Manifold's PATCH_COMMAND. The script deletes the call, re-runs as a no-op on already-patched source, and fails the configure if the code around the call has changed, so a version bump can't silently skip it. CLAUDE.md's Manifold entry records it and says to drop it once we move past #1789.

Tested:

• Fresh AddressSanitizer build, where FetchContent downloads and patches Manifold: all 1354 tests pass, including the Minkowski one (on main it aborts with the overflow).
• Patching paths:
  • re-running the script prints "already applied" and changes nothing;
  • reconfiguring an existing build directory patches its unpatched copy;
  • a changed source fails with a clear message.
• Release build: ctest passes all 2013 tests.

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