fix(auth): return synthetic credentials for noAuth free providers

Requests to opencode (noAuth: true) were failing with "No credentials for
provider: opencode" because getProviderCredentials found no DB connections and
returned null — triggering the 400 error path in chatHelpers.

Inject a synthetic credential object (connectionId: "noauth", no apiKey/token)
before the regular connection lookup so the executor receives valid credentials
and skips the Authorization header. Also enable model import for noAuth providers
(canImportModels = true when isFreeNoAuth).

src/app/(dashboard)/dashboard/providers/[id]/page.tsx

@@ -2542,7 +2542,7 @@ export default function ProviderDetailPage() {
     }
   };
 
-  const canImportModels = connections.some((conn) => conn.isActive !== false);
+  const canImportModels = isFreeNoAuth || connections.some((conn) => conn.isActive !== false);
 
   // Auto-sync toggle state: read from first active connection's providerSpecificData
   const autoSyncConnection = connections.find((conn: any) => conn.isActive !== false);

src/sse/services/auth.ts

@@ -37,7 +37,7 @@ import {
   PROVIDER_ERROR_TYPES,
 } from "@omniroute/open-sse/services/errorClassifier.ts";
 import { getCodexModelScope } from "@omniroute/open-sse/executors/codex.ts";
-import { getProviderAlias, resolveProviderId } from "@/shared/constants/providers";
+import { getProviderAlias, resolveProviderId, FREE_PROVIDERS } from "@/shared/constants/providers";
 import { isModelExcludedByConnection } from "@/domain/connectionModelRules";
 import * as log from "../utils/logger";
 import { fisherYatesShuffle, getNextFromDeckSync } from "@/shared/utils/shuffleDeck";
@@ -770,6 +770,29 @@ export async function getProviderCredentials(
   try {
     await currentMutex;
 
+    // noAuth free providers (e.g. opencode) need no DB connection — return synthetic credentials
+    // so the executor receives a valid credentials object without auth headers being added.
+    const resolvedId = resolveProviderId(provider);
+    if (FREE_PROVIDERS[resolvedId]?.noAuth) {
+      return {
+        apiKey: null,
+        accessToken: null,
+        refreshToken: null,
+        expiresAt: null,
+        projectId: null,
+        copilotToken: null,
+        providerSpecificData: {},
+        connectionId: "noauth",
+        testStatus: "active",
+        lastError: null,
+        lastErrorType: null,
+        lastErrorSource: null,
+        errorCode: null,
+        rateLimitedUntil: null,
+        maxConcurrent: null,
+      };
+    }
+
     const allowSuppressedConnections = options.allowSuppressedConnections === true;
     const bypassQuotaPolicy = options.bypassQuotaPolicy === true;
     const forcedConnectionId =