feat: multi-tenant workspace isolation, RBAC, sidebar nav, billing, and Android enhancements

- Backend: workspace_id isolation for 14 model tables + safe migration/backfill
- Backend: RBAC system with 4 roles and 23 permissions, seeded on startup
- Backend: workspace admin endpoints (list/manage all workspaces)
- Backend: admin user management API (CRUD, reset password)
- Backend: billing API with subscription plans, usage tracking, rate limiting
- Backend: fix system_logs.py UNION query and wrong column references
- Backend: WebSocket JWT auth and workspace enforcement
- Frontend: sidebar navigation replacing top dropdown menu
- Frontend: user management page (Users.vue) for admins
- Frontend: enhanced Workspaces.vue with admin table view
- Frontend: workspace RBAC computed properties in user store
- Android: agent marketplace, billing/subscription UI, onboarding wizard
- Android: phone login, analytics tracker, crash handler, network diagnostics
- Android: splash screen, encrypted token storage, app update enhancements
- Docs: multi-tenant RBAC guide with 8 sections and role-permission matrix

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

backend/app/models/knowledge_entry.py

@@ -3,7 +3,8 @@
 """
 import uuid
 from datetime import datetime
-from sqlalchemy import Column, String, Text, Integer, DateTime, Boolean, JSON, Float, Index
+from sqlalchemy import Column, String, Text, Integer, DateTime, Boolean, JSON, Float, Index, ForeignKey
+from sqlalchemy.dialects.mysql import CHAR
 from app.core.database import Base
 
 
@@ -13,6 +14,7 @@ class KnowledgeEntry(Base):
 
     id = Column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
     agent_id = Column(String(36), nullable=True, index=True, comment="所属 Agent ID（NULL=全Agent共享）")
+    workspace_id = Column(CHAR(36), ForeignKey("workspaces.id"), nullable=True, index=True, comment="工作区ID")
     title = Column(String(500), nullable=False, comment="知识标题（一句话概括）")
     category = Column(String(30), nullable=False, index=True,
                       comment="类别: bug_fix/best_practice/workaround/optimization/insight")
@@ -55,6 +57,7 @@ class KnowledgeEntry(Base):
         return {
             "id": self.id,
             "agent_id": self.agent_id,
+            "workspace_id": self.workspace_id,
             "title": self.title,
             "category": self.category,
             "tags": self.tags or [],