MISSION: support run 6da47ca3, arithmetic-difference-graph arm

This is a hunt. Nothing here is a result, and nothing here is evidence for or against RH (docs/08).

A support run launched by another live run working Erdős #126. The bounded question, as briefed:

Turn $A$ and $-A$ into the bipartite $S$-unit difference pattern $K_{n,n}$ minus the diagonal. Locate and specialize the strongest Győry–Hajdu–Tijdeman or related representation theorems for finite graphs as difference graphs of $S$-units. Track quantitative dependence on $k$ exactly, and determine whether the extra within-part pair-sum structure yields an improvement. Return a theorem-level reduction, not a literature summary. Start from hunts/r_186989/RESULTS.md but audit it.

May write: hunts/support_6da47ca3/ and one case-log entry in hunts/README.md (Hunt #106). May not write: any other hunts/ directory, zeta/, harness/, lean/, meta/, or any root markdown file.

Budget 45 minutes, no operator supervision.