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_content_agent.py

@@ -17,7 +17,7 @@ import uuid
 import json
 
 
-def generate_content_agent(db: Session, username: str = "admin"):
+def generate_content_agent(db: Session, username: str | None = None):
     """生成内容生成助手Agent"""
     print("=" * 60)
     print("生成内容生成助手Agent")
@@ -479,7 +479,7 @@ if __name__ == "__main__":
     import argparse
     
     parser = argparse.ArgumentParser(description="生成内容生成助手Agent")
-    parser.add_argument("--username", type=str, default="admin", help="用户名")
+    parser.add_argument("--username", type=str, default=None, help="用户名")
     
     args = parser.parse_args()