Feature: Support CSV file import in Batch Analytics

Description

🛠️ Before You Raise an Issue

Summary

Currently, the Batch Analytics page only supports uploading usernames via .txt files (one username per line). Many users manage team data in spreadsheets, so adding support for .csv file imports would significantly streamline the workflow.

Current Behavior

• File uploader only accepts .txt files.
• Users must manually convert CSV exports to TXT files before uploading.

Proposed Changes

Modify the file upload logic in src/gitlab_compliance_checker/ui/batch.py to:

1. Update File Uploader: Change type=["txt"] to type=["txt", "csv"].
2. Add CSV Parsing: Use pandas or standard Python csv module to handle .csv files.
   • If it's a CSV, it should ideally look for a column named username or just use the first column if no header is present.
3. Maintain Backward Compatibility: Ensure .txt file uploads and manual text area input continue to work seamlessly.

Acceptance Criteria

•  Users can select and upload a .csv file in the Batch Analytics configuration.
  •  The app correctly extracts usernames from the uploaded CSV.
  •  Error handling is implemented for malformed CSV files.
  •  Manual entry and .txt uploads still function as expected.

Technical Details

• File to modify: src/gitlab_compliance_checker/ui/batch.py
• Logic: Use pd.read_csv(uploaded_file) when the file type is detected as CSV.
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