code-mode: carry nested tool kind through runtime (#22377)

## Why

Code mode only used nested spec lookup at execution time to rediscover
whether a nested tool should be invoked as a function tool or a freeform
tool.

That information is already present in the enabled tool metadata that
code mode builds to expose `tools.*` and `ALL_TOOLS`, so re-looking it
up from the router was redundant and kept execution coupled to a
separate spec lookup path.

## What Changed

- thread `CodeModeToolKind` through the code-mode runtime `ToolCall`
event and `CodeModeNestedToolCall`
- emit the nested tool kind directly from the V8 callback using the
already-enabled tool metadata
- build nested tool payloads from the propagated kind instead of calling
`find_spec`
- remove the now-unused `find_spec` plumbing from the router and
parallel runtime helpers
- add unit coverage for function vs freeform payload shaping and update
affected router tests

## Testing

- `cargo test -p codex-code-mode`
- `cargo test -p codex-core code_mode::tests`
- `cargo test -p codex-core
extension_tool_bundles_are_model_visible_and_dispatchable`
- `cargo test -p codex-core
model_visible_specs_filter_deferred_dynamic_tools`

codex-rs/code-mode/src/service.rs

@@ -385,11 +385,17 @@ async fn run_session_control(
                             text,
                         }).await;
                     }
-                    RuntimeEvent::ToolCall { id, name, input } => {
+                    RuntimeEvent::ToolCall {
+                        id,
+                        name,
+                        kind,
+                        input,
+                    } => {
                         let tool_call = CodeModeNestedToolCall {
                             cell_id: cell_id.clone(),
                             runtime_tool_call_id: id,
                             tool_name: name,
+                            tool_kind: kind,
                             input,
                         };
                         let _ = inner