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/core/src/session/mcp.rs

@@ -1013,6 +1013,7 @@ fn mcp_elicitation_response_from_guardian_decision(
     match decision {
         ReviewDecision::Approved
         | ReviewDecision::ApprovedForSession
+        | ReviewDecision::ApprovedMcpPolicyAmendment
         | ReviewDecision::ApprovedExecpolicyAmendment { .. }
         | ReviewDecision::NetworkPolicyAmendment { .. } => ElicitationResponse {
             action: ElicitationAction::Accept,