feat: documentation update

- Completed export workflow implementation (query builders, CSV/XLSX serializers, streaming API endpoints, UI modals, automated tests).
- Added export modal UI and client script to trigger downloads directly from dashboard.
- Documented import/export field mapping and usage guidelines in FR-008.
- Updated installation guide with export environment variables, dependencies, and CLI/CI usage instructions.

CONTRIBUTING.md

@@ -2,14 +2,42 @@
 
 We welcome contributions to Calminer! If you would like to contribute, please follow these guidelines:
 
-1. **Fork the Repository**: Create a personal copy of the repository on your GitHub account.
+## Fork the Repository
 
-2. **Create a Branch**: Before making changes, create a new branch for your feature or bug fix.
+Create a personal copy of the repository on your GitHub account.
 
-3. **Make Your Changes**: Implement your changes in the new branch.
+## Create a Branch
 
-4. **Write Tests**: Ensure that your changes are covered by tests.
+Before making changes, create a new branch for your feature or bug fix.
 
-5. **Submit a Pull Request**: Once you are satisfied with your changes, submit a pull request to the main repository.
+## Make Your Changes
+
+Implement your changes in the new branch.
+
+## Write Tests
+
+Ensure that your changes are covered by tests.
+
+## Run Test Suite With Coverage
+
+Execute the default pytest run to enforce the 80% project-wide coverage threshold and review missing lines in the terminal report.
+
+```bash
+pytest
+```
+
+## Run Export Test Suite
+
+Before opening a pull request, run the export-focused pytest module to verify CSV/XLSX streaming endpoints.
+
+```bash
+pytest tests/test_export_routes.py
+```
+
+This ensures the API headers, download content, and modal routes remain functional.
+
+## Submit a Pull Request
+
+Once you are satisfied with your changes, submit a pull request to the main repository.
 
 Thank you for your interest in contributing to Calminer!