fix(amux): fall back to default base when AMUX_API_BASE is empty

[duanbing]

What

Restores the empty-AMUX_API_BASE fallback guard on main.

static ref AMUX_API_BASE: String = std::env::var("AMUX_API_BASE")
    .ok()
    .filter(|s| !s.is_empty())                       // ← restored
    .unwrap_or_else(|| "https://api.amux.ai".to_string());

Why

main currently uses the naive form:

std::env::var("AMUX_API_BASE").unwrap_or_else(|_| "https://api.amux.ai".to_string())

unwrap_or_else only fires on Err (var missing). An env var set to the empty string returns Ok("") and slips through, leaving AMUX_API_BASE = "" — a broken base URL. That's exactly what docker-compose produces with AMUX_API_BASE: ${AMUX_API_BASE:-} when the host var is unset.

The fix shipped on feat/amux-seedance (cff4cfb) but was lost when the amux provider was squash-merged to main as #12 (1e9dc55). This cherry-picks just that commit back onto main so the default wins on an empty value as well as a missing one.

Context

Consumed downstream by RouterBase/RouterBase#143 (submodule bump). Once this lands on main, a future RouterBase pin can track the submodule's main cleanly instead of the feat/amux-seedance SHA.

🤖 Generated with Claude Code

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