FJRW-ThreeBlock-F: Problem Statement and Reconstruction Boundary Tables for the Three-Block Thom-Sebastiani Sum F = W + W + W

Standalone dataset and formal problem specification (`docs/PROBLEM.md`, `docs/RECONSTRUCTION_BOUNDARY.md`, `docs/WHAT_THIS_IS_NOT.md`, `tables/block_comparison.csv`, `tables/not_closed_by_concavity.csv`) for the Fan-Jarvis-Ruan-Witten (FJRW) cohomological field theory of the three-block Thom-Sebastiani sextic polynomial F = W (+) W (+) W with chain atom W = u^5 v + v^6. Defines the three-block FJRW problem and explicitly tabulates the correlators that lie beyond pure concavity axioms; does not claim an unproved closed-form evaluation of open mixed correlators. Copyright (c) 2026 Benjamin Stanley Frohman. Licensed under the Apache License, Version 2.0.