fix(web): scope markdown actions to their environment

Use the owning thread or pull request environment for editor, shell, and remote-open actions instead of whichever environment is active. Add a multi-environment regression test for the action hooks.

Audit: R20

Implemented by GPT-5.6 Sol with Codex.
00d2b33214Julius Marminge committed on 9/1/2026, 4:32:53 AMparent6007bc4
2 files changedLine totals unavailable