[codex-apps] Filter optional file fields by tool schema (#31686)

## Summary

Codex Apps file parameters are exposed to the model as local paths,
uploaded at execution time, and rewritten into provided-file payloads
before the MCP tool call.

The rewrite currently includes the documented optional fields
`mime_type` and `file_name` for every file parameter. Apps with strict
schemas can reject those fields when they are not declared.

## Changes

- Derive the supported optional file fields from each
`openai/fileParams` parameter's raw input schema before replacing it
with the model-visible local-path schema.
- Always include `download_url` and `file_id`.
- Include `mime_type` and `file_name` only when that specific file
parameter's schema accepts them, including schemas that allow additional
properties.
- Handle scalar and array file parameters, including items-only arrays,
composed schemas, and local JSON Schema references.
- Preserve the existing restriction that only the host-owned Codex Apps
MCP server can use this upload path.

This supports tools with different file contracts in the same app: one
parameter can accept the optional fields while another remains strict.

## Validation

- `just test -p codex-mcp`
- `just test -p codex-core mcp_openai_file`
- `just test -p codex-core codex_apps_file_params_`
- `just fix -p codex-mcp`
- `just fix -p codex-core`
- `just fmt`
- `git diff --check`
- Manually verified in the Codex Electron app that:
  - a strict file schema receives only `download_url` and `file_id`
  - a rich file schema also receives `mime_type` and `file_name`

Related: #31330

codex-rs/codex-mcp/src/codex_apps.rs

@@ -5,6 +5,11 @@
 
 use codex_utils_plugins::mcp_connector::sanitize_name;
 
+mod file_params;
+
+pub use file_params::declared_openai_file_input_param_names;
+pub(crate) use file_params::prepare_openai_file_params_for_model;
+
 pub(crate) fn normalize_codex_apps_tool_title(connector_name: Option<&str>, value: &str) -> String {
     let Some(connector_name) = connector_name
         .map(str::trim)