Add plumbing to approve stored Auto-Review denials (#18955)

## Summary

This adds the structural plumbing needed for an app-server client to
approve a previously denied Guardian review and carry that approval
context into the next model turn.

This PR does not add the actual `/auto-review-denials` tool 

## What Changed

- Added app-server v2 RPC `thread/approveGuardianDeniedAction`.
- Added generated JSON schema and TypeScript fixtures for
`ThreadApproveGuardianDeniedAction*`.
- Added core `Op::ApproveGuardianDeniedAction`.
- Added a core handler that validates the event is a denied Guardian
assessment and injects a developer message containing the stored denial
event JSON.
- Queues the approval context for the next turn if there is no active
turn yet.
- Added the TUI app-server bridge so `Op::ApproveGuardianDeniedAction {
event }` is routed to the app-server request.

## What This Does Not Do

- Does not add `/auto-review-denials`.
- Does not add chat widget recent-denial state.
- Does not add popup/list UI.
- Does not add a product-facing denial lookup/store.
- Does not change where Guardian denials are originally emitted or
persisted.

## Verification

- `cargo test -p codex-tui thread_approve_guardian_denied_action`

codex-rs/app-server-protocol/schema/json/v2/ThreadApproveGuardianDeniedActionResponse.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "ThreadApproveGuardianDeniedActionResponse",
+  "type": "object"
+}