feat: Implement backend core functionality for news-engine-console

Phase 1 Backend Implementation:
- ✅ MongoDB data models (Keyword, Pipeline, User, Application)
- ✅ Pydantic schemas for all models with validation
- ✅ KeywordService: Full CRUD, filtering, pagination, stats, toggle status
- ✅ PipelineService: Full CRUD, start/stop/restart, logs, config management
- ✅ Keywords API: 8 endpoints with complete functionality
- ✅ Pipelines API: 11 endpoints with complete functionality
- ✅ Updated TODO.md to reflect completion

Key Features:
- Async MongoDB operations with Motor
- Comprehensive filtering and pagination support
- Pipeline logging system
- Statistics tracking for keywords and pipelines
- Proper error handling with HTTP status codes
- Type-safe request/response models

Files Added:
- models/: 4 data models with PyObjectId support
- schemas/: 4 schema modules with Create/Update/Response patterns
- services/: KeywordService (234 lines) + PipelineService (332 lines)

Files Modified:
- api/keywords.py: 40 → 212 lines (complete implementation)
- api/pipelines.py: 25 → 300 lines (complete implementation)
- TODO.md: Updated checklist with completed items

Next Steps:
- UserService with authentication
- ApplicationService for OAuth2
- MonitoringService
- Redis integration
- Frontend implementation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

services/news-engine-console/backend/app/models/user.py

@@ -0,0 +1,49 @@
+from datetime import datetime
+from typing import Optional
+from pydantic import BaseModel, Field, EmailStr
+from bson import ObjectId
+
+
+class PyObjectId(ObjectId):
+    """Custom ObjectId type for Pydantic"""
+    @classmethod
+    def __get_validators__(cls):
+        yield cls.validate
+
+    @classmethod
+    def validate(cls, v):
+        if not ObjectId.is_valid(v):
+            raise ValueError("Invalid ObjectId")
+        return ObjectId(v)
+
+    @classmethod
+    def __get_pydantic_json_schema__(cls, field_schema):
+        field_schema.update(type="string")
+
+
+class User(BaseModel):
+    """User data model for authentication and authorization"""
+
+    id: Optional[PyObjectId] = Field(default=None, alias="_id")
+    username: str = Field(..., min_length=3, max_length=50)
+    email: EmailStr = Field(...)
+    hashed_password: str = Field(...)
+    full_name: str = Field(..., min_length=1, max_length=100)
+    role: str = Field(default="viewer", description="Role: admin, editor, viewer")
+    disabled: bool = Field(default=False)
+    created_at: datetime = Field(default_factory=datetime.utcnow)
+    last_login: Optional[datetime] = None
+
+    class Config:
+        populate_by_name = True
+        arbitrary_types_allowed = True
+        json_encoders = {ObjectId: str}
+        json_schema_extra = {
+            "example": {
+                "username": "johndoe",
+                "email": "johndoe@example.com",
+                "full_name": "John Doe",
+                "role": "editor",
+                "disabled": False
+            }
+        }