feat: Add MiniMax Anthropic-compatible API support (minimax-api)

Add --auth-choice minimax-api for direct MiniMax API usage at
https://api.minimax.io/anthropic using the anthropic-messages API.

Changes:
- Add applyMinimaxApiConfig() function with provider/model config
- Add minimax-api to AuthChoice type and CLI options
- Add handler and non-interactive support
- Fix duplicate minimax entry in envMap
- Update live test to use anthropic-messages API
- Add 11 unit tests covering all edge cases
- Document configuration in gateway docs

Test results:
- 11/11 unit tests pass
- 1/1 live API test passes (verified with real API key)

Co-Authored-By: Claude <noreply@anthropic.com>

src/commands/auth-choice.ts

@@ -36,6 +36,8 @@ import {
 } from "./google-gemini-model-default.js";
 import {
   applyAuthProfileConfig,
+  applyMinimaxApiConfig,
+  applyMinimaxApiProviderConfig,
   applyMinimaxConfig,
   applyMinimaxHostedConfig,
   applyMinimaxHostedProviderConfig,
@@ -629,6 +631,24 @@ export async function applyAuthChoice(params: {
       agentModelOverride = "lmstudio/minimax-m2.1-gs32";
       await noteAgentModel("lmstudio/minimax-m2.1-gs32");
     }
+  } else if (params.authChoice === "minimax-api") {
+    const key = await params.prompter.text({
+      message: "Enter MiniMax API key",
+      validate: (value) => (value?.trim() ? undefined : "Required"),
+    });
+    await setMinimaxApiKey(String(key).trim(), params.agentDir);
+    nextConfig = applyAuthProfileConfig(nextConfig, {
+      profileId: "minimax:default",
+      provider: "minimax",
+      mode: "api_key",
+    });
+    if (params.setDefaultModel) {
+      nextConfig = applyMinimaxApiConfig(nextConfig);
+    } else {
+      nextConfig = applyMinimaxApiProviderConfig(nextConfig);
+      agentModelOverride = "minimax/MiniMax-M2.1";
+      await noteAgentModel("minimax/MiniMax-M2.1");
+    }
   }
 
   return { config: nextConfig, agentModelOverride };