Remove deprecated rollout conversation list aliases

[andrei-hasna]

Summary

• Removed the deprecated rollout-list aliases ConversationItem = ThreadItem and ConversationsPage = ThreadsPage from codex-rs/rollout/src/list.rs.
• Compatibility decision: the aliases were not re-exported by codex-rollout; list is pub(crate) and the public surface already exposes ThreadItem and ThreadsPage.
• No internal code was switched back to the old conversation names.

Validation

• rg -n '\bConversationItem\b|\bConversationsPage\b' codex-rs/rollout codex-rs/core sdk macos codex-cli README.md docs --glob '!codex-rs/rollout/src/list.rs' --glob '!codex-rs/rollout-trace/**' returned no matches.
• cd codex-rs && just check-fast -p codex-rollout passed.
• cd codex-rs && just test-fast -p codex-rollout passed: nextest run dbffc054-235b-4606-b954-5030f25f2f90, 70 tests passed.
• cd codex-rs && just fix -p codex-rollout passed.
• cd codex-rs && UV_CACHE_DIR=/tmp/codewith-uv-cache just fmt passed. Plain just fmt first hit a read-only home uv cache after Rust formatter completed.
• gitleaks protect --staged --config .gitleaks.toml --redact --no-banner passed: no leaks found.

Adversarial Review

• Read-only verifier 019f38a6-7130-7213-a30a-bdd400027253 reported no findings.
• Reviewer confirmed the alias removal is compatible with module/export visibility, no hidden in-repo uses remain, the branch diff contains only codex-rs/rollout/src/list.rs, and validation covers the scoped acceptance.

Residual risk: out-of-repo consumers were not tested, but the removed aliases were not externally reachable through the crate API.

Task: fb334b63-36a1-4d0b-babd-09913099a0f4