Extract hooks into dedicated crate (#11311)

Summary
- move `core/src/hooks` implementation into a new `codex-hooks` crate
with its own manifest
- update `codex-rs` workspace and `codex-core` crate to depend on the
extracted `hooks` crate and wire up the shared APIs
- ensure references, modules, and lockfile reflect the new crate layout

Testing
- Not run (not requested)

codex-rs/core/src/lib.rs

@@ -37,7 +37,6 @@ pub mod features;
 mod file_watcher;
 mod flags;
 pub mod git_info;
-pub mod hooks;
 pub mod instructions;
 pub mod landlock;
 pub mod mcp;