Update guardian output schema (#17061)

## Summary
- Update guardian output schema to separate risk, authorization,
outcome, and rationale.
- Feed guardian rationale into rejection messages.
- Split the guardian policy into template and tenant-config sections.

## Validation
- `cargo test -p codex-core mcp_tool_call`
- `env -u CODEX_SANDBOX_NETWORK_DISABLED INSTA_UPDATE=always cargo test
-p codex-core guardian::`

---------

Co-authored-by: Owen Lin <owen@openai.com>

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -4854,16 +4854,18 @@
             }
           ]
         },
-        "riskScore": {
-          "format": "uint8",
-          "minimum": 0.0,
-          "type": [
-            "integer",
-            "null"
-          ]
-        },
         "status": {
           "$ref": "#/definitions/GuardianApprovalReviewStatus"
+        },
+        "userAuthorization": {
+          "anyOf": [
+            {
+              "$ref": "#/definitions/GuardianUserAuthorization"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "required": [
@@ -5061,6 +5063,17 @@
     "GuardianRiskLevel": {
       "description": "[UNSTABLE] Risk level assigned by guardian approval review.",
       "enum": [
+        "low",
+        "medium",
+        "high",
+        "critical"
+      ],
+      "type": "string"
+    },
+    "GuardianUserAuthorization": {
+      "description": "[UNSTABLE] Authorization level assigned by guardian approval review.",
+      "enum": [
+        "unknown",
         "low",
         "medium",
         "high"