feat(engine): answer texts with Codex as well as Claude Code

• 80a7c827a0 fix(security): only honour iMessage, because SMS sender IDs are spoofable glennmichael123 review this step
• 77017da95c feat(engine): add CodexEngine, and give Engine an identity and a probe glennmichael123 review this step
• f0960e120f feat: select the engine per installation, and report on the one selected glennmichael123 review this step
• ddc2096ae1 chore: tidy import order in the engine factory and the buddy command glennmichael123 review this step
• a45830ffa2 fix: give every popover check an informational flag, and assert on the whole argv glennmichael123 review this step