[codex] Stream chat panel responses

[bradvin]

Summary

This branch switches the main ClawPress chat panel to real streaming responses and simplifies the runtime around that flow.

• add bradvin/wp-ai-client-streaming integration for the main chat panel
• add /chat/stream SSE delivery and update the panel client to consume streamed deltas directly
• replace the old transport abstraction with a single Agent_Event_Sink
• normalize no-argument tool schemas so provider calls like file_list no longer fail
• add PHPUnit AI client stubs so the test suite no longer depends on the old Composer AI client package
• pin the Plugin Check CI job to WordPress 7.0 via wp-env

Why

ClawPress already supports streaming, so the previous panel-side streaming mimic layer was unnecessary complexity. This change moves the main chat flow onto true streamed deltas, fixes the provider schema edge cases exposed by no-arg tools, and aligns CI with the WordPress 7 runtime assumptions required by Plugin Check.

Validation

• vendor/bin/phpunit --configuration phpunit.xml.dist
• npm run lint:php
• npm run build

Notes

• build:pot still emits the pre-existing translators-comment warning in includes/functions.php
• I did not run a manual browser chat session in CI