Add configurable hook context spill limits (#34393)

## What changed

- Add `additionalContextLimit` to command hook configuration for events that can emit `additionalContext`.
- Apply the limit independently to each hook's context before it is sent to the model. Unset values retain the 2,500-token default, while `0` disables spilling for that hook.
- Expose configured limits through app-server hook and requirements responses, and show them in the TUI hooks browser.

## Testing

- Cover JSON and TOML parsing, discovery and hashing, per-hook spilling behavior, app-server responses, and TUI rendering.

GitOrigin-RevId: 55ddc2dbbdf9067dceee3e1968c03617bbf6bcea

codex-rs/core/src/session/tests.rs

@@ -1503,6 +1503,7 @@ async fn refresh_runtime_config_refreshes_hooks() -> anyhow::Result<()> {
                     timeout_sec: Some(600),
                     r#async: false,
                     status_message: None,
+                    additional_context_limit: None,
                 }],
             },
         };