Add website support for Claude-compatible skill distributions

[snissn]

Summary

This PR implements PR 3 from issue #13 on top of PR #15.

It makes the website distribution-aware while preserving the current canonical Markdown pack browsing flow.

What changed

• updated scripts/sync-agents-static.js to:
  • sync distributions/ into website static assets
  • generate website/src/generated/distribution-index.json
  • parse canonical 0.4.0 pack metadata for better display on the site
• updated /agents to surface Claude-compatible skill availability per pack
• added a new /agents/skill route for inspecting generated skill bundles
• added a skill bundle viewer with:
  • rendered SKILL.md
  • supporting file list
  • selected file rendering
  • canonical-pack linkout and file download affordances
• added supporting utility and styling updates

Validation

• node scripts/sync-agents-static.js
• npm run build

Notes

• canonical /agents/spec flow remains intact
• this PR does not change MCP behavior
• PR remains stacked on the compiler work in Add pack-to-Claude-skill compiler and pilot outputs #15

Refs #13