Heck Freezes Over v31 — Double Middle Ring

Seven starts retained from v30; each has three +2 home mex.
The original eight +1.2 mex remain exactly where they were in v30.
One additional +1.2 mex sits beside each original, yielding eight pairs / 16 ring mex.
Three +6 mex in the pit stay unchanged.
Terrain SMF/SMT, feature placements, starts, tree and rock reclaim are byte-for-byte unchanged from v30.
The newly placed mex were checked against the heightmap for local terrain relief, but require in-game buildability tests.
