Findings from the FILT150 run: (1) scattered rank-150 selection starved the
per-scene neighbor consolidation (min_str_neib/eig_str_neib) - only ~57 tiles
with accidental neighbors were measured per scene (neighbors-vs-measured
corr 0.78); (2) roll degraded (RMS 0.106 vs 0.059 mrad, bias +0.073) - the
selection carried only 11% of the full set's roll information.

deriveSelection() stage 2 now picks disjoint 3x3 CLUSTERS of gate-passing
tiles (>=CLUSTER_MIN_ELIGIBLE=6 of 9), round-robin from three pools:
LEFTMOST, RIGHTMOST (per Andrey - edge tiles have the most roll influence),
BEST-QUALITY (median member fmax), until the tile budget is filled; scattered
best tiles fill any remainder. Offline simulation on the real calibration:
24 clusters (8/8/8), 150 tiles, mean 3.97 in-selection neighbors, roll info
+48% vs scattered rank-150. Measurement code untouched (oracle identical).

mvn compile clean.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>