chore: add December 19, 2025 release notes and update catalog to dcp56

[Copilot]

Plan for December 19, 2025 Release Updates

• Add new release notes section to docs/dcp-updates.mdx with December 19, 2025 date
  • Add 4 new projects with correct links
  • Add 1 updated project with correct link
  • Follow existing formatting convention (Markdown links)
• Update default catalog from dcp55 to dcp56
  • Update CATALOG constant in site-config/data-portal/dev/config.ts
• Address review feedback
  • Convert HTML anchor tags to Markdown links to match existing format

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update dcp-updates.mdx: Add new release notes for 2025-12-19 and set default catalog to dcp56</issue_title>
<issue_description>Please update the docs/dcp-updates.mdx file with a new section for today's release following the existing format. Here are the details to add:

December 19, 2025

New projects (4):

1. A multi-omics atlas of the human retina at single-cell resolution
2. Asian Immune Diversity Atlas (AIDA): Asian diversity in human immune cells (Thailand cells)
3. Single cell atlas of the human retina
4. Single-cell multiomics of the human retina reveals hierarchical transcription factor collaboration in mediating cell type-specific effects of genetic variants on gene regulation

Updated Projects (1):

1. Spatial transcriptomic profiling of human retinoblastoma

Also update the default catalog reference in the repository from dcp55 to dcp56 wherever it appears (such as environment or config files) as part of this release.

Please ensure the notes are inserted with today's date and match the formatting of previous releases.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update dcp-updates.mdx: Add new release notes for 2025-12-19 and set default catalog to dcp56 #2870

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[MillenniumFalconMechanic]

@copilot, can you update the new and updated project links added in this PR to be markdown and not HTML?

[Copilot]

Already done in b396398 - all links are now using Markdown format [text](url) instead of HTML anchor tags.