Connect ads for a platform

Unified ads connection endpoint. Handles all platforms through a single route: **Same-token platforms** (facebook, instagram, linkedin): If a posting account already exists, returns `alreadyConnected: true` immediately (no extra OAuth needed). If not, starts the normal OAuth flow, and the resulting account supports both posting and ads. **Separate-token platforms** (tiktok, twitter, pinterest): Requires an existing posting account (`accountId` param). If ads are already connected, returns `alreadyConnected: true`. Otherwise, starts the platform-specific marketing API OAuth flow. **Ads-only platforms** (googleads): If a Google Ads account exists, returns `alreadyConnected: true`. Otherwise, starts the Google Ads OAuth flow. Use the `adsStatus` field from `GET /v1/accounts` to check which accounts need ads connection.

curl -X GET "https://zernio.com/api/v1/connect/facebook/ads?profileId=string"

{
  "alreadyConnected": true,
  "accountId": "664a1b2c3d4e5f6789012345",
  "platform": "instagram",
  "username": "@mybrand",
  "displayName": "My Brand"
}

{
  "error": "Unauthorized"
}