Derive sandbox contexts from turn environments (#40551)

## What changed

- Add Windows sandbox mode, private-desktop behavior, and legacy Landlock selection to each `EnvironmentConfig`.
- Centralize sandbox context construction on `TurnEnvironment`, preserving environment-owned permissions, paths, and backend settings while applying additional permission grants.
- Use the environment-derived context for project instructions, capability discovery, file uploads, and filesystem-oriented tools.

## Testing

- Verify capability discovery uses the selected environment's permission profile and sandbox backends when they differ from the thread defaults.

GitOrigin-RevId: 7ae2fed90c8ada950f2e8431e571e9b2c793c291

codex-rs/core/src/mcp_tool_call.rs

@@ -773,6 +773,8 @@ async fn augment_mcp_tool_request_meta_with_sandbox_state(
     else {
         return Ok(meta);
     };
+    // TODO(anp): Build this metadata from the server's captured
+    // TurnEnvironment::sandbox_context instead of the runtime-wide Landlock value.
     let permission_profile = prepared_call.config().permission_profile.clone();
     let sandbox_state = serde_json::to_value(SandboxState {
         permission_profile,