feat: workspace CRUD at platform scope + drop audit_logs

新增系统管理模块 /api/v1/platform/*:
- workspace 实体 CRUD(创建/列表/详情/更新/软删除)
- workspace 成员 CRUD(添加/列表/更新/移除)
- SystemAdminContext 依赖,仅 platform_role_id 指向 admin 角色的用户可访问
- /api/v1/auth/me 与 /auth/login 增 is_system_admin 派生字段
- 不变量:每个 workspace 至少保留一个 admin;系统管理员无法自我移除成员
- 软删除 workspace 级联软删除其成员

清理 audit_logs(无运行时写入,纯死特性):
- baseline 移除 audit_logs 建表与三索引(20 → 19 tables)
- 删除 AuditLogs 模型定义与 __init__.py 导出
- 清理 migrate_system_json / migrate_legacy_workspaces 中的 audit 写入与回填代码

API.md 增 §七系统管理,§七/§八/§九 顺延为 §八/§九/§十,附录 A/B 同步更新。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

common/src/common/db/models/__init__.py

@@ -1,5 +1,4 @@
 from common.db.base import Base
-from common.db.models.audit import AuditLogs
 from common.db.models.events import ConsumerInbox, OutboxEvents
 from common.db.models.identity import Permissions, RolePermissions, Roles, Users
 from common.db.models.runtime import WorkspaceOperations
@@ -16,7 +15,6 @@ from common.db.models.workspaces import WorkspaceMembers, Workspaces
 
 __all__ = [
     "Base",
-    "AuditLogs",
     "ConsumerInbox",
     "DataResources",
     "OutboxEvents",

common/src/common/db/models/audit.py

@@ -1,38 +0,0 @@
-import datetime
-from typing import Optional
-
-from sqlalchemy import Index, JSON, String, text
-from sqlalchemy.dialects.mysql import BIGINT, CHAR, DATETIME, TINYINT
-from sqlalchemy.orm import Mapped, mapped_column
-
-from common.db.base import Base
-
-
-class AuditLogs(Base):
-    __tablename__ = "audit_logs"
-    __table_args__ = (
-        Index("idx_audit_action_time", "action_code", "created_at"),
-        Index("idx_audit_actor_time", "actor_user_id", "created_at"),
-        Index("idx_audit_workspace_time", "workspace_id", "created_at"),
-        {"comment": "操作审计日志"},
-    )
-
-    audit_id: Mapped[int] = mapped_column(BIGINT, primary_key=True)
-    action_code: Mapped[str] = mapped_column(String(128), nullable=False)
-    target_type: Mapped[str] = mapped_column(String(64), nullable=False)
-    operation_status: Mapped[str] = mapped_column(
-        String(16), nullable=False, server_default=text("'success'")
-    )
-    created_at: Mapped[datetime.datetime] = mapped_column(
-        DATETIME(fsp=3), nullable=False, server_default=text("CURRENT_TIMESTAMP(3)")
-    )
-    workspace_id: Mapped[Optional[str]] = mapped_column(CHAR(26))
-    actor_user_id: Mapped[Optional[str]] = mapped_column(CHAR(26))
-    target_id: Mapped[Optional[str]] = mapped_column(String(128))
-    client_ip: Mapped[Optional[str]] = mapped_column(String(45))
-    user_agent: Mapped[Optional[str]] = mapped_column(String(1000))
-    detail_json: Mapped[Optional[dict]] = mapped_column(JSON)
-    is_deleted: Mapped[int] = mapped_column(
-        TINYINT(1), nullable=False, server_default=text("0")
-    )
-    deleted_at: Mapped[Optional[datetime.datetime]] = mapped_column(DATETIME(fsp=3))