fix(xai): inline local refs and broaden codex app tool normalization

- Export `InlineLocalRefs` utility to resolve local JSON Pointer references.
- Inline local definitions and remove `$defs`/`definitions` in tool function parameters.
- Support `mcp__` prefixes and `codex_apps` namespace variations when identifying Codex app automation update tools.
- Handle `$ref` entries when inspecting and normalizing root union schema branches.