Remove client_common tool re-exports (#16482)

## Why

`codex-rs/core/src/client_common.rs` still had a `tools` re-export
module that forwarded `codex_tools` types back into `codex-core`. After
the earlier extraction work in #16379, #16471, #16477, and #16481, that
extra layer no longer adds value.

Removing it keeps dependencies explicit: the `codex-core` modules that
actually use `ToolSpec` and related types now depend on `codex_tools`
directly instead of reaching through `client_common`.

## What Changed

- removed the `client_common::tools` re-export module from
`core/src/client_common.rs`
- updated the remaining `codex-core` consumers to import `codex_tools`
directly
- adjusted the affected test code to reference
`codex_tools::ResponsesApiTool` directly as well

This is a mechanical cleanup only. It does not change tool behavior or
runtime logic.

## Testing

- `cargo test -p codex-core client_common::tests`
- `cargo test -p codex-core tools::router::tests`
- `cargo test -p codex-core tools::context::tests`
- `cargo test -p codex-core tools::spec::tests`

codex-rs/core/src/tools/js_repl/mod.rs

@@ -31,7 +31,6 @@ use tracing::trace;
 use tracing::warn;
 use uuid::Uuid;
 
-use crate::client_common::tools::ToolSpec;
 use crate::codex::Session;
 use crate::codex::TurnContext;
 use crate::exec::ExecCapturePolicy;
@@ -46,6 +45,7 @@ use codex_sandboxing::SandboxCommand;
 use codex_sandboxing::SandboxManager;
 use codex_sandboxing::SandboxTransformRequest;
 use codex_sandboxing::SandboxablePreference;
+use codex_tools::ToolSpec;
 use codex_utils_output_truncation::TruncationPolicy;
 use codex_utils_output_truncation::truncate_text;