feat(core) Add login to shell_command tool (#6846)

## Summary
Adds the `login` parameter to the `shell_command` tool - optional,
defaults to true.

## Testing
- [x] Tested locally

codex-rs/core/src/tools/spec.rs

@@ -331,6 +331,15 @@ fn create_shell_command_tool() -> ToolSpec {
             description: Some("The working directory to execute the command in".to_string()),
         },
     );
+    properties.insert(
+        "login".to_string(),
+        JsonSchema::Boolean {
+            description: Some(
+                "Whether to run the shell with login shell semantics. Defaults to true."
+                    .to_string(),
+            ),
+        },
+    );
     properties.insert(
         "timeout_ms".to_string(),
         JsonSchema::Number {