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/hooks/src/engine/dispatcher.rs

@@ -236,6 +236,7 @@ mod tests {
             command: command.to_string(),
             timeout_sec: 5,
             status_message: None,
+            additional_context_limit: Default::default(),
             source_path: test_path_buf("/tmp/hooks.json").abs(),
             source: HookSource::User,
             display_order,