fix: classification results empty and res.data access issues

Backend:
- Add GET /classifications/results endpoint with project/level/keyword filters
- Add column relationship to ClassificationResult model
- Fix test data generator to fetch column IDs from DB after bulk insert

Frontend:
- Fix request.ts interceptor to return full response body (keep total/pagination)
- Fix all pages to use res.data instead of res
- Add getClassificationResults API in classification.ts
- Implement fetchData in Classification.vue with proper filtering and pagination
- Fix same res.data issue in Category.vue, Metadata.vue, Project.vue, DataSource.vue, Dashboard.vue, Task.vue

backend/app/models/project.py

@@ -92,6 +92,7 @@ class ClassificationResult(Base):
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
 
     project = relationship("ClassificationProject", back_populates="results")
+    column = relationship("DataColumn")
     category = relationship("Category")
     level = relationship("DataLevel")