Forwards `api_mode`, `acp_command`, `acp_args`, and `credential_pool` from the resolved runtime provider into `AIAgent.__init__()` in the WebUI streaming path. Fixes Codex account switching and credential pool support for WebUI sessions. Also adds 6 defensive variable initializations to prevent NameError in cleanup paths.
Tests: 1329 passed, 0 skipped. Full TestRuntimeRouteInjection suite passes.
PR by @suinia. Rebased and CHANGELOG added by maintainer.
Co-authored-by: suinia <suinia@users.noreply.github.com>