DBP-38: Allow saving users' submit result

[pan93412]

• feat: add submission model
• chore: generate ent code
• refactor: update SubmissionResult definition
• feat: implement submission API

[linear]

DBP-38 Allow saving users' submit result

[Copilot]

Pull Request Overview

This PR implements submission functionality allowing users to save their SQL query submission results. The changes include adding a submission model, implementing a submission service with answer validation, and integrating it with the GraphQL API.

• Add submission domain models: Introduces SQLExecutionResult and UserSQLExecutionResult for storing query results and comparison status
• Implement submission service: Creates service to handle answer submission, validation against reference answers, and persistence
• Integration with GraphQL API: Adds submitAnswer mutation and updates resolver structure to support submission functionality

Reviewed Changes

Copilot reviewed 60 out of 60 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
models/submission.go	Defines submission result data structures
internal/submission/submission.go	Core submission service with answer validation logic
internal/submission/submission_test.go	Comprehensive test suite for submission functionality
internal/testhelper/sqlrunner.go	Test helpers for SQL runner container setup
graph/question.resolvers.go	GraphQL resolver for submitAnswer mutation
ent/schema/submission.go	Database schema definition for submissions
Multiple ent/ files	Generated Ent ORM code for submission entity

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