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/mod.rs

@@ -2597,7 +2597,8 @@ impl Session {
                         strict_auto_review: false,
                     },
                 },
-                ReviewDecision::Abort
+                ReviewDecision::ApprovedMcpPolicyAmendment
+                | ReviewDecision::Abort
                 | ReviewDecision::Denied { .. }
                 | ReviewDecision::TimedOut => RequestPermissionsResponse {
                     permissions: RequestPermissionProfile::default(),