feat(fb): implement submission CRUD service

[muratmuzaffer]

What does this PR do?

Implements the submission service layer for managing form submissions as specified in issue #48.

Added

• SubmissionService class in services/form/app/services/submission_service.py
• Three core async methods:
  • create_submission() - Creates submission with form validation
  • get_submission_by_id() - Retrieves submission by ID
  • get_submissions_by_form_id() - Paginated submission list (default: 10, max: 100)
• Form validation:
  • Checks if form exists
  • Checks if form is active
  • Checks if form has started (start_date)
  • Checks if deadline has not passed (deadline)
• Atomic submission_count increment on form
• Export from app/services/__init__.py

Technical Details

• All methods use async/await pattern
• Uses Motor async driver for MongoDB operations
• Uses await cursor.to_list(length=limit) for pagination
• Raises ValueError for business logic errors
• Re-raises PyMongoError for database errors
• Handles timezone-naive/aware datetime comparison

Related Issue

Closes #48

Checklist

• Code follows project conventions
• I tested my changes locally
• Linting passes
• I added @seberatolmez or @DogukanUrker as reviewers

[DogukanUrker]

WAY better than the prev. PR - just have a few things to consider. than we good to go. good job!!

[muratmuzaffer]

.env.example deletion
Reverted. the file is now restored. Sorry for the scope creep!

Regarding ObjectId.is_valid() validation
Added validation as suggested. Now raises ValueError for invalid ObjectId strings instead of bson.errors.InvalidId, keeping error handling consistent with the rest of the service.

[DogukanUrker]

looks good now, you can merge it whenever

[muratmuzaffer]

Thanks for the feedback!