feat(remote-control): add pairing status transport (#26449)

## What

Adds transport support for checking remote-control pairing status
against the backend.

- Adds the normalized `server/pair/status` backend URL.
- Adds backend request/response structs for exactly one lookup key:
`pairing_code` or `manual_pairing_code`, returning `{ claimed }`.
- Adds `RemoteControlEnrollment::pairing_status` and
`RemoteControlHandle::pairing_status`.
- Preserves auth refresh/retry behavior and backend error mapping.
- Adds transport coverage for pending, claimed, manual-code payloads,
token refresh, mapped backend errors, malformed responses, and URL
normalization.

## Why

Desktop needs a host-authenticated way to poll whether a QR or manual
pairing code has been claimed.

Related backend change: https://github.com/openai/openai/pull/990244

## Verification

- `cargo test --manifest-path app-server-transport/Cargo.toml
remote_control::tests::pairing_tests`
- `cargo fmt --all --check`
- `git diff --check`

codex-rs/app-server-protocol/src/protocol/v2/remote_control.rs

@@ -62,6 +62,23 @@ pub struct RemoteControlPairingStartResponse {
     pub expires_at: i64,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct RemoteControlPairingStatusParams {
+    #[ts(optional = nullable)]
+    pub pairing_code: Option<String>,
+    #[ts(optional = nullable)]
+    pub manual_pairing_code: Option<String>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct RemoteControlPairingStatusResponse {
+    pub claimed: bool,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]