AC-ADMIN-CONFIG-002: File Type Configuration

### AC-ADMIN-CONFIG-002: File Type Configuration

**Priority**: P2
**Type**: Acceptance Test
**Estimated Time**: 20 min
**Automated Test**: Yes candidate

#### Description
Admin can manage which file types are allowed for upload.

#### Acceptance Criteria
- [ ] Supported file types list with checkboxes:
- [ ] PDF ✓
- [ ] DOCX ✓
- [ ] XLSX ✓
- [ ] JPG ✓
- [ ] PNG ✓
- [ ] CSV ✓
- [ ] ZUGFeRD ✓
- [ ] XRechnung (XML) ✓
- [ ] Each type has enable/disable toggle
- [ ] Admin can check/uncheck each type
- [ ] Save configuration
- [ ] **Upload Validation**:
- [ ] Disabled types rejected on upload
- [ ] Error: "File type not allowed: CSV"
- [ ] Enabled types accepted
- [ ] Validation by MIME type + extension (security)
#### Test Steps
1. Navigate to Document Portal Settings
2. Uncheck "CSV" and "ZUGFeRD"
3. Save
4. Test upload CSV file
5. Verify error: "File type not allowed"
6. Test upload PDF file
7. Verify success
8. Re-enable CSV
9. Save
10. Test upload CSV file
11. Verify success