[app-server] feat: export.rs supports a v2 namespace, initial v2 notifications (#6212)

**Typescript and JSON schema exports**
While working on Thread/Turn/Items type definitions, I realize we will
run into name conflicts between v1 and v2 APIs (e.g. `RateLimitWindow`
which won't be reusable since v1 uses `RateLimitWindow` from `protocol/`
which uses snake_case, but we want to expose camelCase everywhere, so
we'll define a V2 version of that struct that serializes as camelCase).

To set us up for a clean and isolated v2 API, generate types into a
`v2/` namespace for both typescript and JSON schema.
- TypeScript: v2 types emit under `out_dir/v2/*.ts`, and root index.ts
now re-exports them via `export * as v2 from "./v2"`;.
- JSON Schemas: v2 definitions bundle under `#/definitions/v2/*` rather
than the root.

The location for the original types (v1 and types pulled from
`protocol/` and other core crates) haven't changed and are still at the
root. This is for backwards compatibility: no breaking changes to
existing usages of v1 APIs and types.

**Notifications**
While working on export.rs, I:
- refactored server/client notifications with macros (like we already do
for methods) so they also get exported (I noticed they weren't being
exported at all).
- removed the hardcoded list of types to export as JSON schema by
leveraging the existing macros instead
- and took a stab at API V2 notifications. These aren't wired up yet,
and I expect to iterate on these this week.

codex-rs/app-server/src/codex_message_processor.rs

@@ -4,6 +4,7 @@ use crate::fuzzy_file_search::run_fuzzy_file_search;
 use crate::models::supported_models;
 use crate::outgoing_message::OutgoingMessageSender;
 use crate::outgoing_message::OutgoingNotification;
+use codex_app_server_protocol::AccountRateLimitsUpdatedNotification;
 use codex_app_server_protocol::AccountUpdatedNotification;
 use codex_app_server_protocol::AddConversationListenerParams;
 use codex_app_server_protocol::AddConversationSubscriptionResponse;
@@ -625,7 +626,9 @@ impl CodexMessageProcessor {
     async fn get_account_rate_limits(&self, request_id: RequestId) {
         match self.fetch_account_rate_limits().await {
             Ok(rate_limits) => {
-                let response = GetAccountRateLimitsResponse { rate_limits };
+                let response = GetAccountRateLimitsResponse {
+                    rate_limits: rate_limits.into(),
+                };
                 self.outgoing.send_response(request_id, response).await;
             }
             Err(error) => {
@@ -1766,7 +1769,9 @@ async fn apply_bespoke_event_handling(
             if let Some(rate_limits) = token_count_event.rate_limits {
                 outgoing
                     .send_server_notification(ServerNotification::AccountRateLimitsUpdated(
-                        rate_limits,
+                        AccountRateLimitsUpdatedNotification {
+                            rate_limits: rate_limits.into(),
+                        },
                     ))
                     .await;
             }