app-server service tier plumbing (plus some cleanup) (#13334)

followup to https://github.com/openai/codex/pull/13212 to expose fast
tier controls to app server
(majority of this PR is generated schema jsons - actual code is +69 /
-35 and +24 tests )

- add service tier fields to the app-server protocol surfaces used by
thread lifecycle, turn start, config, and session configured events
- thread service tier through the app-server message processor and core
thread config snapshots
- allow runtime config overrides to carry service tier for app-server
callers

cleanup:
- Removing useless "legacy" code supporting "standard" - we moved to
None | "fast", so "standard" is not needed.

codex-rs/core/src/codex_thread.rs

@@ -9,6 +9,7 @@ use crate::protocol::Event;
 use crate::protocol::Op;
 use crate::protocol::Submission;
 use codex_protocol::config_types::Personality;
+use codex_protocol::config_types::ServiceTier;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseInputItem;
 use codex_protocol::models::ResponseItem;
@@ -27,6 +28,7 @@ use crate::state_db::StateDbHandle;
 pub struct ThreadConfigSnapshot {
     pub model: String,
     pub model_provider_id: String,
+    pub service_tier: Option<ServiceTier>,
     pub approval_policy: AskForApproval,
     pub sandbox_policy: SandboxPolicy,
     pub cwd: PathBuf,