## Why
This is part 3 of a 7-PR stack to remove direct
`codex_protocol::protocol` usage from `codex-tui` while keeping each
layer reviewable and shippable.
With `AppCommand` now explicit, the internal app event bus can carry TUI
commands directly instead of bouncing through core `Op` values.
## What changed
- Changed `AppEvent::CodexOp` and `AppEvent::SubmitThreadOp` to carry
`AppCommand`.
- Updated app-event senders and direct emitters to submit `AppCommand`
values.
- Adjusted tests to match `AppCommand` or convert back through
`into_core()` where they intentionally assert legacy payload equality.
## Verification
- `cargo test -p codex-tui --no-run`
Eric TrautandGitHub
d0204c3dcc