MiniMax Token Plan (Plus) keys fail with 401 - broken China endpoint auto-detection

Bug Description

MiniMax Token Plan (Plus/Max/Ultra) API keys start with sk-cp- prefix but work on the international endpoint (api.minimax.io), NOT the China endpoint (api.minimaxi.com).

The current auto-detection in jcode incorrectly routes sk-cp- keys to the China endpoint, causing 401 authentication errors.

Reproduction

1. Get a MiniMax Token Plan (Plus) subscription
2. Configure jcode with the Plus plan API key
3. Try to use MiniMax-M2.7 model
4. Get 401 Unauthorized error

Root Cause

In crates/jcode-base/src/provider_catalog.rs:

if key.trim_start().starts_with("sk-cp-") {
    resolved.api_base = MINIMAX_CHINA_API_BASE.to_string();  // WRONG!
}

Fix

Remove the China auto-detection - Token Plan keys work on international endpoint. See PR: https://github.com/ChathurangaBW/jcode/pull/new/fix/minimax-token-plan-endpoint

Alternative: Add JCODE_MINIMAX_API_BASE env var override (already implemented in fix branch).

Verification

curl -X POST "https://api.minimax.io/v1/chat/completions" \
  -H "Authorization: Bearer sk-cp-YOUR_TOKEN" \
  -d '{"model": "MiniMax-M2.7", "messages": [{"role": "user", "content": "test"}]}'  

Returns successful response on international endpoint.

Start in crates/jcode-base/src/provider_catalog.rs and inspect the MiniMax API-base resolution for keys beginning with sk-cp-. Use the curl verification request in the issue to confirm the international endpoint accepts the key; done means MiniMax Token Plan keys no longer route to the China endpoint and the documented request succeeds.