Sync fork with upstream CollectionBuilder-CSV: Apply key accessibility and bug fixes while preserving custom features

[Copilot]

This PR selectively syncs the forschung.stadtgeschichtebasel.ch fork with upstream CollectionBuilder-CSV, applying critical accessibility improvements and bug fixes while preserving all Stadt.Geschichte.Basel custom features.

Background

The fork had diverged significantly from upstream (622 commits behind, 275 files differing) due to extensive customizations including multi-language support, EDTF timeline functionality, geodata visualization, and Stadt.Geschichte.Basel-specific branding. A full merge would have created hundreds of conflicts and risked breaking custom functionality.

Changes Applied

1. Fixed Blank Cloud Items Bug

Problem: Tag clouds could display empty items when metadata fields contained null values.
Solution: Added | compact filter in _includes/js/cloud-js.html to remove empty values before processing.

// Before
{% assign new = items | map: c | join: ';' %}

// After  
{% assign new = items | map: c | compact | join: ';' %}

2. Improved Accessibility with Correct ARIA Controls

Problem: Download buttons had incorrect aria-controls attributes pointing to generic "collapseExample" instead of actual target IDs.
Solution: Updated aria-controls to match the actual collapse target IDs for better screen reader navigation.

// Before
aria-controls="collapseExample"

// After
aria-controls="collapseTranscript"
aria-controls="collapseTranscript{{ child.objectid }}"

3. Enhanced TimelineJS Accessibility

Problem: TimelineJS timeline data lacked alt text for images, reducing accessibility.
Solution: Added alt text fields to assets/data/timelinejs.json using metadata or fallback values.

{
  "media": {
    "url": "...",
    "alt": {{ item.image_alt_text | default: item.description | default: item.title | jsonify }},
    "caption": "..."
  }
}

Custom Features Preserved

All Stadt.Geschichte.Basel customizations remain intact:

• Multi-language support (German/Spanish translations)
• EDTF timeline with custom sort plugin
• Interactive geodata maps with Swiss coordinate system support
• Custom layout and navigation structure
• Trigger warning functionality
• Report button for metadata issues
• GitHub Actions CI/CD workflows
• Prettier code formatting standards

Strategy & Risk Mitigation

• Selective cherry-picking instead of bulk merge to avoid conflicts
• Minimal changes focused on high-value, low-risk improvements
• Preserved compatibility with existing Stadt.Geschichte.Basel infrastructure
• Documented upstream commits for future reference and maintenance

This approach enables the project to benefit from upstream improvements while maintaining the significant investment in custom development that makes this platform unique for historical research data presentation.

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