feat(agent): add online verification and governing-answer citations

Claim-bound online verification observations with URL provenance, exact
answer-basis references for citation-free governing-rule answers, and an
explicit operator identity handoff before source transfer. Bounds resumed
work by learning unit and refreshes pack manifest/contracts.

contracts/schemas/ReadEnvelope.schema.json

@@ -313,6 +313,19 @@
       "title": "Data",
       "type": "array"
     },
+    "filtered_count": {
+      "anyOf": [
+        {
+          "minimum": 0,
+          "type": "integer"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "default": null,
+      "title": "Filtered Count"
+    },
     "index_revision": {
       "anyOf": [
         {