bridge: route unknown models to claude runtime for ANTHROPIC_MODEL users

[honghaoaa1230]

Problem

When users connect via kittylitter and use third-party models through ANTHROPIC_MODEL (DeepSeek, OpenRouter, Mimo, etc.), selecting those models in Litter fails because:

1. runtime_for_model_hint() does not recognize third-party model names (e.g., deepseek-v4-pro[1m], mimo-v2) — they route to "codex" by default instead of "claude"
2. runtime_for_thread_start() has no fallback: when both resolve_model_selection() and runtime_for_model_hint() return None, it always defaults to "codex", even when the claude runtime is connected

Proposed fix

Two changes in shared/rust-bridge/codex-mobile-client/src/mobile_client/mod.rs:

1. Add common third-party provider patterns to runtime_for_model_hint()

_ if normalized.contains("deepseek") => Some("claude".to_string()),
_ if normalized.contains("openrouter") => Some("claude".to_string()),

2. Add claude runtime fallback in runtime_for_thread_start()

When no model hint matches, check if the claude runtime is connected and prefer it over the codex default:

if let Ok(session) = self.get_session(server_id) {
    let runtimes = session.runtime_kinds();
    if runtimes.iter().any(|k| k == "claude") {
        return "claude".to_string();
    }
}
"codex".to_string()

Why this is safe

• The fallback only activates when claude runtime is explicitly connected
• The existing explicit runtime override (explicit_runtime_kind) still takes priority
• Model names not in available_models are passed through unchanged to the host, where Claude Code handles them via ANTHROPIC_MODEL

Related

Companion fix needed in dnakov/alleycat: the Claude bridge model/list handler should advertise ANTHROPIC_MODEL env var values so custom models appear in the Litter model picker.