## Why
This addresses the review comment from #17751 about `marketplace/remove`
app-server test portability:
https://github.com/openai/codex/pull/17751#discussion_r3104378613
The API returns the removed installed root using the app-server's
effective `CODEX_HOME`. On macOS, temporary directory paths can appear
as either `/var/...` or `/private/var/...`, so comparing one raw path
against another can fail even when `marketplace/remove` behaves
correctly.
## What changed
- Removed the direct whole-response equality assertion for the installed
root path.
- Asserted the stable response field, `marketplace_name`, directly.
- Compared the expected and returned installed-root paths after
canonicalizing their existing parent directories, which avoids requiring
the removed leaf directory to still exist.
## Verification
- `cargo test -p codex-app-server
marketplace_remove_deletes_config_and_installed_root`
- `cargo test -p codex-app-server marketplace_remove`
## Summary
Add a new app-server `marketplace/remove` RPC on top of the shared
marketplace-remove implementation.
This change:
- adds `MarketplaceRemoveParams` / `MarketplaceRemoveResponse` to the
app-server protocol
- wires the new request through `codex_message_processor`
- reuses the shared core marketplace-remove flow from the stacked
refactor PR
- updates generated schema files and adds focused app-server coverage
## Validation
- `just write-app-server-schema`
- `just fmt`
- heavy compile/test coverage deferred to GitHub CI per request
