[Codex][CLI] Gate image inputs by model modalities (#10271)

###### Summary

- Add input_modalities to model metadata so clients can determine
supported input types.
- Gate image paste/attach in TUI when the selected model does not
support images.
- Block submits that include images for unsupported models and show a
clear warning.
- Propagate modality metadata through app-server protocol/model-list
responses.
  - Update related tests/fixtures.

  ###### Rationale

  - Models support different input modalities.
- Clients need an explicit capability signal to prevent unsupported
requests.
- Backward-compatible defaults preserve existing behavior when modality
metadata is absent.

  ###### Scope

  - codex-rs/protocol, codex-rs/core, codex-rs/tui
  - codex-rs/app-server-protocol, codex-rs/app-server
  - Generated app-server types / schema fixtures

  ###### Trade-offs

- Default behavior assumes text + image when field is absent for
compatibility.
  - Server-side validation remains the source of truth.

  ###### Follow-up

- Non-TUI clients should consume input_modalities to disable unsupported
attachments.
- Model catalogs should explicitly set input_modalities for text-only
models.

  ###### Testing

  - cargo fmt --all
  - cargo test -p codex-tui
  - env -u GITHUB_APP_KEY cargo test -p codex-core --lib
  - just write-app-server-schema
- cargo run -p codex-cli --bin codex -- app-server generate-ts --out
app-server-types
  - test against local backend
  
<img width="695" height="199" alt="image"
src="https://github.com/user-attachments/assets/d22dd04f-5eba-4db9-a7c5-a2506f60ec44"
/>

---------

Co-authored-by: Josh McKinney <joshka@openai.com>

codex-rs/core/tests/suite/remote_models.rs

@@ -25,6 +25,7 @@ use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::openai_models::ReasoningEffortPreset;
 use codex_protocol::openai_models::TruncationPolicyConfig;
+use codex_protocol::openai_models::default_input_modalities;
 use codex_protocol::user_input::UserInput;
 use core_test_support::load_default_config_for_test;
 use core_test_support::responses::ev_assistant_message;
@@ -76,6 +77,7 @@ async fn remote_models_remote_model_uses_unified_exec() -> Result<()> {
         shell_type: ConfigShellToolType::UnifiedExec,
         visibility: ModelVisibility::List,
         supported_in_api: true,
+        input_modalities: default_input_modalities(),
         priority: 1,
         upgrade: None,
         base_instructions: "base instructions".to_string(),
@@ -313,6 +315,7 @@ async fn remote_models_apply_remote_base_instructions() -> Result<()> {
         shell_type: ConfigShellToolType::ShellCommand,
         visibility: ModelVisibility::List,
         supported_in_api: true,
+        input_modalities: default_input_modalities(),
         priority: 1,
         upgrade: None,
         base_instructions: remote_base.to_string(),
@@ -787,6 +790,7 @@ fn test_remote_model_with_policy(
         shell_type: ConfigShellToolType::ShellCommand,
         visibility,
         supported_in_api: true,
+        input_modalities: default_input_modalities(),
         priority,
         upgrade: None,
         base_instructions: "base instructions".to_string(),