Config: add MiniMax direct API authentication option

Makes apiKey optional in ModelProviderConfig so MiniMax can use auth
profiles or environment variables (MINIMAX_API_KEY) instead of requiring
explicit config.

Changes:
- src/config/types.ts: apiKey changed from required to optional
- src/config/zod-schema.ts: use z.string().min(1).optional() for validation
- src/commands/configure.ts: add minimax-api auth choice in wizard
- src/commands/onboard-auth.ts: MiniMax provider omits apiKey (uses env/auth)
- patches/@mariozechner__pi-ai@0.42.1.patch: map minimax → MINIMAX_API_KEY

Auth Resolution Order (unchanged):
1. Auth profiles (highest priority)
2. Environment variables (MINIMAX_API_KEY, etc.)
3. Custom provider apiKey from models.json (lowest priority)

src/commands/configure.ts

@@ -70,6 +70,7 @@ import { healthCommand } from "./health.js";
 import { formatHealthCheckFailure } from "./health-format.js";
 import {
   applyAuthProfileConfig,
+  applyMinimaxApiConfig,
   applyMinimaxConfig,
   applyMinimaxHostedConfig,
   applyOpencodeZenConfig,
@@ -369,6 +370,7 @@ async function promptAuthConfig(
     | "gemini-api-key"
     | "apiKey"
     | "minimax-cloud"
+    | "minimax-api"
     | "minimax"
     | "opencode-zen"
     | "skip";
@@ -788,6 +790,21 @@ async function promptAuthConfig(
     next = applyMinimaxHostedConfig(next);
   } else if (authChoice === "minimax") {
     next = applyMinimaxConfig(next);
+  } else if (authChoice === "minimax-api") {
+    const key = guardCancel(
+      await text({
+        message: "Enter MiniMax API key",
+        validate: (value) => (value?.trim() ? undefined : "Required"),
+      }),
+      runtime,
+    );
+    await setMinimaxApiKey(String(key).trim());
+    next = applyAuthProfileConfig(next, {
+      profileId: "minimax:default",
+      provider: "minimax",
+      mode: "api_key",
+    });
+    next = applyMinimaxApiConfig(next);
   } else if (authChoice === "opencode-zen") {
     note(
       [

src/commands/onboard-auth.ts

@@ -336,7 +336,7 @@ export function applyMinimaxApiProviderConfig(
   const providers = { ...cfg.models?.providers };
   providers.minimax = {
     baseUrl: MINIMAX_API_BASE_URL,
-    apiKey: "", // Resolved via MINIMAX_API_KEY env var or auth profile
+    // apiKey omitted: resolved via MINIMAX_API_KEY env var or auth profile by default.
     api: "anthropic-messages",
     models: [buildMinimaxApiModelDefinition(modelId)],
   };