rv64im_min_multi_tier_roi.nx

rv64im_min_multi_tier_roi.nx -- per-tier ROI matrix + ranker. Extends rv64im_min_hot_report.nx (commit 772abfb) from single- workload ROI to multi-tier ROI per the WORKLOAD_TARGETS.md + hardened-field-not-just-AI cardinal. Input: one NxFuncCycles report per workload tier (W0/W1/W2) Output: ranked list of silicon candidates with per-tier ROI vectors + min-across-tiers + weighted-sum aggregate The killer constraint per WORKLOAD_TARGETS.md: "Sovereign silicon needs to serve the whole workload set, not over-fit one. Avoids the trap of adding a 7000-gate vector MAC unit because it triples GEMM throughput, but doubles silicon cost for the sprinkler controller that never uses it." So the ranker offers TWO views: min_across_tiers -- pick the candidate whose worst tier still has positive ROI. Conservative; ensures no tier is starved. weighted_sum -- pick the candidate whose operator-weighted ROI sum is highest. Lets the operator tune ("W0 matters 4x more than W2 because field deployments outnumber data center units 1000-to-1"). Status: SEED. 2026-05-26. Multi-tier matrix builder + dual rankers. Future commits add temporal weighting (recency of measurement) + confidence intervals (sim-vs-silicon delta).