packaging: README (NASA style) + possibilistic perf baseline + CI benchmark job

README: purpose-first (possibility not boolean, caller owns evidence/time),
install, verified quick start, concepts (result shape, overlays, temporal
context), API table, development commands, design notes.

benchmark: scripts/benchmark.js on @tenere/benchmark-lib — eight contours
(direct/union/denied/meta/overlay/binary checks, snapshot build/restore),
committed .rigor-baseline.json, exit 1 on high-severity regressions.

CI: benchmark job compares on push (continue-on-error), re-saves baseline
and uploads it as an artifact on tags; publish now depends on benchmark
passing as well as test.

package-lock.json

@@ -15,6 +15,7 @@
       },
       "devDependencies": {
         "@rigor/core": "*",
+        "@tenere/benchmark-lib": "^2.0.1",
         "fast-check": "^4.5.3",
         "peggy": "^5.0.6"
       }
@@ -305,6 +306,17 @@
         "node": ">=18.0.0"
       }
     },
+    "node_modules/@tenere/benchmark-lib": {
+      "version": "2.0.1",
+      "resolved": "https://hub.kl1.tenere.ai/api/packages/Tenere/npm/%40tenere%2Fbenchmark-lib/-/2.0.1/benchmark-lib-2.0.1.tgz",
+      "integrity": "sha512-ZM+bAVmrg9r/4vrCkNd5sIxQtSzfKOZcg8XFACPhPNajNQDO10VFPzukQrjJ4bmD7Poc4iplAHujKPoH6GXirQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@rigor/core": "^3.0.4",
+        "@rigor/search": "^0.1.2"
+      }
+    },
     "node_modules/@tenere/graph-core": {
       "version": "1.0.1",
       "resolved": "https://hub.kl1.tenere.ai/api/packages/Tenere/npm/%40tenere%2Fgraph-core/-/1.0.1/graph-core-1.0.1.tgz",