Extract run control store interface

[chubes4]

Summary

• Add a generic WP_Agent_Run_Control_Store contract for run-control state persistence.
• Move the current option-backed persistence into WP_Agent_Option_Run_Control_Store.
• Keep WP_Agent_Run_Control as the compatibility facade while allowing store injection.
• Add smoke coverage for injectable store behavior through the existing facade.

Verification

• php tests/workflow-runner-smoke.php
• composer run phpstan
• composer run smoke
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the store extraction, focused smoke coverage, and verification workflow; Chris remains responsible for review and merge.