feat: implement backend API clients for multi-marketplace integration and frontend service layer

backend/routes/credentials.py

@@ -0,0 +1,59 @@
+# backend/routes/credentials.py
+from flask import Blueprint, request, jsonify
+from datetime import datetime
+import json
+
+from ..db import get_db_connection, release_db_connection
+
+credentials_blueprint = Blueprint('credentials', __name__)
+
+@credentials_blueprint.route('/credentials', methods=['GET'])
+def list_credentials():
+    """Return configured platforms (without exposing secrets)."""
+    conn = get_db_connection()
+    cur = conn.cursor()
+    cur.execute("SELECT platform FROM credentials")
+    rows = cur.fetchall()
+    release_db_connection(conn)
+    
+    platforms = [r[0] for r in rows]
+    return jsonify({"configured_platforms": platforms})
+
+@credentials_blueprint.route('/credentials/<string:platform>', methods=['POST'])
+def save_credentials(platform):
+    """Save or update credentials for a specific platform."""
+    data = request.json
+    api_key = data.get('api_key')
+    client_id = data.get('client_id')
+    client_secret = data.get('client_secret')
+    other_data = data.get('other_data', {})
+    
+    conn = get_db_connection()
+    cur = conn.cursor()
+    
+    cur.execute(
+        """INSERT INTO credentials (platform, api_key, client_id, client_secret, other_data, updated_at)
+           VALUES (%s, %s, %s, %s, %s, %s)
+           ON CONFLICT (platform) DO UPDATE SET 
+               api_key = EXCLUDED.api_key,
+               client_id = EXCLUDED.client_id,
+               client_secret = EXCLUDED.client_secret,
+               other_data = EXCLUDED.other_data,
+               updated_at = EXCLUDED.updated_at""",
+        (platform, api_key, client_id, client_secret, json.dumps(other_data), datetime.utcnow())
+    )
+    conn.commit()
+    release_db_connection(conn)
+    
+    return jsonify({"message": f"Credentials for {platform} saved successfully."}), 200
+
+@credentials_blueprint.route('/credentials/<string:platform>', methods=['DELETE'])
+def delete_credentials(platform):
+    """Delete credentials for a specific platform."""
+    conn = get_db_connection()
+    cur = conn.cursor()
+    cur.execute("DELETE FROM credentials WHERE platform = %s", (platform,))
+    conn.commit()
+    release_db_connection(conn)
+    
+    return jsonify({"message": f"Credentials for {platform} deleted."}), 200