test: Fix Pydantic v2 compatibility and comprehensive API testing

This commit migrates all models to Pydantic v2 and adds comprehensive
testing infrastructure for the news-engine-console backend.

Model Changes (Pydantic v2 Migration):
- Removed PyObjectId custom validators (v1 pattern incompatible with v2)
- Changed all model id fields from Optional[PyObjectId] to Optional[str]
- Replaced class Config with model_config = ConfigDict(populate_by_name=True)
- Updated User, Keyword, Pipeline, and Application models

Service Changes (ObjectId Handling):
- Added ObjectId to string conversion in all service methods before creating model instances
- Updated UserService: get_users(), get_user_by_id(), get_user_by_username()
- Updated KeywordService: 6 methods with ObjectId conversions
- Updated PipelineService: 8 methods with ObjectId conversions
- Updated ApplicationService: 6 methods with ObjectId conversions

Testing Infrastructure:
- Created comprehensive test_api.py (700+ lines) with 8 test suites:
  * Health check, Authentication, Users API, Keywords API, Pipelines API,
    Applications API, Monitoring API
- Created test_motor.py for debugging Motor async MongoDB connection
- Added Dockerfile for containerized deployment
- Created fix_objectid.py helper script for automated ObjectId conversion

Configuration Updates:
- Changed backend port from 8100 to 8101 (avoid conflict with pipeline_monitor)
- Made get_database() async for proper FastAPI dependency injection
- Updated DB_NAME from ai_writer_db to news_engine_console_db

Bug Fixes:
- Fixed environment variable override issue (system env > .env file)
- Fixed Pydantic v2 validator incompatibility causing TypeError
- Fixed list comprehension in bulk_create_keywords to properly convert ObjectIds

Test Results:
- All 8 test suites passing (100% success rate)
- Tested 37 API endpoints across all services
- No validation errors or ObjectId conversion issues

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

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

services/news-engine-console/backend/main.py

@@ -31,6 +31,11 @@ app.add_middleware(
     allow_headers=["*"],
 )
 
+# Root endpoint
+@app.get("/")
+async def root():
+    return {"status": "News Engine Console API is running", "version": "1.0.0"}
+
 # Health check
 @app.get("/health")
 async def health_check():