Restructure solution layout by module

src/Bench/StellaOps.Bench/LinkNotMerge.Vex/README.md

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+# Link-Not-Merge VEX Bench
+
+Measures synthetic VEX observation ingest and event emission throughput for the Link-Not-Merge program.
+
+## Scenarios
+
+`config.json` defines workloads with varying statement density and tenant fan-out. Metrics captured per scenario:
+
+- Total latency (ingest + correlation) and p95/max percentiles
+- Correlator-only latency and Mongo insert latency
+- Observation throughput (observations/sec)
+- Event emission throughput (events/sec)
+- Peak managed heap allocations
+
+## Running locally
+
+```bash
+dotnet run \
+  --project src/Bench/StellaOps.Bench/LinkNotMerge.Vex/StellaOps.Bench.LinkNotMerge.Vex/StellaOps.Bench.LinkNotMerge.Vex.csproj \
+  -- \
+  --csv out/linknotmerge-vex-bench.csv \
+  --json out/linknotmerge-vex-bench.json \
+  --prometheus out/linknotmerge-vex-bench.prom
+```
+
+The benchmark exits non-zero if latency thresholds are exceeded, observation or event throughput drops below configured floors, allocations exceed the ceiling, or regression ratios breach the baseline.