chore: upgrade to Rust 1.92.0 (#8860)

**Summary**
- Upgrade Rust toolchain used by CI to 1.92.0.
- Address new clippy `derivable_impls` warnings by deriving `Default`
for enums across protocol, core, backend openapi models, and
windows-sandbox setup.
- Tidy up related test/config behavior (originator header handling, env
override cleanup) and remove a now-unused assignment in TUI/TUI2 render
layout.

**Testing**
- `just fmt`
- `just fix -p codex-tui`
- `just fix -p codex-tui2`
- `just fix -p codex-windows-sandbox`
- `cargo test -p codex-tui`
- `cargo test -p codex-tui2`
- `cargo test -p codex-windows-sandbox`
- `cargo test -p codex-core --test all`
- `cargo test -p codex-app-server --test all`
- `cargo test -p codex-mcp-server --test all`
- `cargo test --all-features`

.github/workflows/rust-release.yml

@@ -80,7 +80,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v6
-      - uses: dtolnay/rust-toolchain@1.90
+      - uses: dtolnay/rust-toolchain@1.92
         with:
           targets: ${{ matrix.target }}