fix(ci): repair non-app-server Rust lint failures

[andrei-hasna]

Why

The full Rust CI matrix on 2968352abd33e7bf6e6a3fd1024b52fd481299da exposed mechanical lint failures outside the concurrently owned app-server and goal-runtime files: argument comments on opaque positional literals, three Rust 1.97 macOS formatting borrows, and Windows-only dead-code diagnostics for Unix policy material.

What changed

• Add the exact /*param_name*/ comments reported by argument-comment-lint outside codex-rs/app-server/** and codex-rs/state/src/runtime/goals.rs.
• Remove the three redundant borrows around Path::display() in the macOS seatbelt assertions.
• Gate Unix-only policy FDs, size limits, secure-file variants, helpers, and the config import with platform cfgs while retaining parser coverage under cfg(test).
• Do not add blanket dead-code allowances and do not modify either excluded ownership area.

Verification

• Owned-scope Bazel argument-comment lint: 668 targets passed.
• Full just argument-comment-lint: only the 11 concurrently owned codex-rs/state/src/runtime/goals.rs diagnostics remain.
• just check-fast -p codex-core
• just test-fast -p codex-core tools::policy::tests (23 passed)
• just test-fast -p codex-sandboxing (50 passed)
• Independent adversarial review: GO, no P0/P1/P2 findings.

The local Windows target check could not reach codex-core because this Linux host lacks x86_64-w64-mingw32-gcc; the native Windows matrix remains the proof gate for that cfg path.

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