Fix proxy failover status output

[apple-ouyang]

Summary

Fixes #143.

This updates the CLI proxy output so it no longer hard-codes automatic failover as disabled. The proxy runtime already reads per-app auto_failover_enabled and routes through the configured failover queue when enabled, so the old message was misleading.

Changes:

• Show a neutral local-proxy mode description in cc-switch proxy show.
• Print per-app automatic failover status for Claude, Codex, and Gemini.
• Make cc-switch proxy serve print the configured automatic failover status instead of saying it is disabled.
• Add a regression test that enables Codex auto failover and verifies the CLI status output reflects it.

Tests

• cargo fmt --all
• cargo test cli::commands::proxy::tests::proxy_overview_lines --lib
• cargo test proxy::provider_router::tests --lib

Note: cargo test --lib on my local macOS environment still has two unrelated proxy runtime/session failures that reproduce when run individually. One fails because a local cc-switch process is already listening on 127.0.0.1:15721; the other is managed_session_ready_info_accepts_persisted_session_without_status_probe.

[unive3sal]

Hi @apple-ouyang

Thanks for your contribution! Would you please rebase your commit for review?

[apple-ouyang]

Rebased, should be OK now. Please take another look.

[SaladDay]

LGTM, cc @unive3sal