feat: P0 commercial readiness — password security, legal, account management

Backend changes for Phase A of v1.0 commercial launch:

P0-3: Password Security
- Remove hardcoded admin/123456 defaults from 34+ bootstrap scripts
- Add PLATFORM_USERNAME/PLATFORM_PASSWORD env vars to config
- Add PUT /api/v1/auth/change-password endpoint (requires old password)

P0-1: User Agreement & Privacy Policy
- Add agreed_terms/agreed_terms_version/agreed_terms_at to User model
- New GET /api/v1/legal/privacy and GET /api/v1/legal/terms endpoints
- New POST /api/v1/legal/agree endpoint to record consent
- Register endpoint now validates agreed_terms must be True

P0-6: Account Management
- Add phone/status/is_email_verified to User model
- Add DELETE /api/v1/auth/account for account deletion (with password confirmation)
- Add PUT /api/v1/auth/phone for phone binding
- Reject authentication for deleted accounts (status=deleted)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/scripts/generate_complex_agent.py

@@ -15,7 +15,7 @@ from datetime import datetime
 import uuid
 
 
-def generate_complex_agent_with_templates(db: Session, username: str = "admin"):
+def generate_complex_agent_with_templates(db: Session, username: str | None = None):
     """生成包含多个节点模板的复杂Agent"""
     print("=" * 60)
     print("生成复杂Agent（包含多个节点模板）")
@@ -292,7 +292,7 @@ if __name__ == "__main__":
     parser.add_argument(
         "--username",
         type=str,
-        default="admin",
+        default=None,
         help="创建Agent的用户名（默认: admin）"
     )