1- Add model service tiers metadata (#20969)

## Why

The model list needs to carry display-ready service tier metadata so
clients can render tier choices with stable IDs, names, and
descriptions. A raw speed-tier string list is not enough for richer UI
copy or future tier labels.

## What changed

- Added `ModelServiceTier` to shared model metadata with string `id`,
`name`, and `description` fields.
- Added `service_tiers` to `ModelInfo` and `ModelPreset`, preserving
empty defaults for older cached model payloads.
- Exposed `serviceTiers` on app-server v2 `Model` responses and threaded
it through TUI app-server model conversion.
- Marked legacy `additional_speed_tiers` / `additionalSpeedTiers`
metadata as deprecated in source and generated schema output.
- Regenerated app-server protocol JSON schema and TypeScript fixtures,
including `ModelServiceTier.ts`.

## Verification

- Ran `just write-app-server-schema`.
- Did not run local tests per repo instruction; relying on PR CI.

---------

Co-authored-by: Codex <noreply@openai.com>

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

@@ -1,6 +1,7 @@
 use std::sync::Arc;
 
 use codex_app_server_protocol::Model;
+use codex_app_server_protocol::ModelServiceTier;
 use codex_app_server_protocol::ModelUpgradeInfo;
 use codex_app_server_protocol::ReasoningEffortOption;
 use codex_core::ThreadManager;
@@ -43,6 +44,15 @@ fn model_from_preset(preset: ModelPreset) -> Model {
         input_modalities: preset.input_modalities,
         supports_personality: preset.supports_personality,
         additional_speed_tiers: preset.additional_speed_tiers,
+        service_tiers: preset
+            .service_tiers
+            .into_iter()
+            .map(|service_tier| ModelServiceTier {
+                id: service_tier.id,
+                name: service_tier.name,
+                description: service_tier.description,
+            })
+            .collect(),
         is_default: preset.is_default,
     }
 }