Add visual applications directory

[santoshkumarradha]

What changed

• Replaces the text-only application list with a purpose-first, three-category visual directory.
• Adds 12 linked 512px thumbnails for the public application catalogue.
• Keeps repository acronyms out of tile labels while retaining links to each repository.

Validation

• Verified all 12 assets are square and referenced from the profile README.
• Verified every tile target resolves to its intended public Agent-Field repository.
• Reviewed the local desktop and narrow layout.