Use ReviewDecision for MCP tool approvals (#38081)

## What changed

- Add `ApprovedMcpPolicyAmendment` to represent MCP approvals that persist across sessions.
- Route MCP approval responses directly through the shared `ReviewDecision` type while preserving session-only approvals, rejection reasons, timeouts, and cancellations.
- Reject the MCP-only policy decision if it reaches command, shell, network, or other tool approval paths.

## Testing

- Update MCP approval parsing, normalization, hook, and Guardian tests for the shared decisions.
- Verify generic tool approvals reject MCP policy amendments.

GitOrigin-RevId: b8cc931dc61d4c794915145273ede82b9eb30fc8

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

@@ -4258,6 +4258,13 @@
           ],
           "type": "string"
         },
+        {
+          "description": "User has approved this MCP tool call and wants to amend its policy so matching future calls are automatically approved across sessions.",
+          "enum": [
+            "approved_mcp_policy_amendment"
+          ],
+          "type": "string"
+        },
         {
           "additionalProperties": false,
           "description": "User chose to persist a network policy rule (allow/deny) for future requests to the same host.",