[codex] Support Anthropic-compatible base URLs

[2233admin]

Closes #325

Summary

• Honor ANTHROPIC_BASE_URL for non-OAuth direct Anthropic Messages requests and model-catalog refreshes.
• Add ANTHROPIC_AUTH_TOKEN support for bearer-token Anthropic-compatible gateways/proxies.
• Preserve existing behavior for Claude OAuth and official Anthropic API keys: OAuth stays on the official OAuth endpoint, and API keys keep using x-api-key.
• Update Anthropic auth-status detection and test env isolation so bearer-token direct auth is visible without polluting unrelated tests.

Validation

• cargo test -p jcode-base provider::anthropic --lib
• cargo test -p jcode-base provider::models::catalog --lib
• cargo test -p jcode-base auth::active_method --lib
• cargo test -p jcode-base full_and_fast_auth_status_match_for_shared_probe_fields --lib
• cargo check -p jcode-base --all-targets
• rustfmt --edition 2024 --config skip_children=true --check <touched Rust files>

Local notes

• cargo fmt --all -- --check reports unrelated formatting churn in untouched modules with my local stable Rust 1.96 checkout.
• cargo clippy -p jcode-base --lib -- -D warnings currently stops on pre-existing warnings outside this patch (jcode-core/src/stdin_detect.rs, jcode-render-core/src/markdown.rs).
• cargo check -p jcode-base --all-targets --all-features is not a clean Windows local signal here: it stops in tikv-jemalloc-sys before checking this patch because the Windows/MSVC all-features path expects a Unix sh/jemalloc configure environment.