fix(render): use portable paths for embedded templates

[BittuBarnwal7479]

📝 Summary

Fix built-in Helm and Terraform template discovery on Windows by using path.Join instead of filepath.Join for paths consumed by embed.FS.

embed.FS implements Go's io/fs, which always expects forward-slash (/) separated paths regardless of the operating system. This change restores correct template loading on Windows while preserving existing behavior on Linux and macOS.

🧩 Type of change

• 🔧 CLI / Go code
• 📦 Helm chart
• 🧱 Terraform module
• 📝 Documentation
• 🧪 Test or CI change
• ♻️ Refactor / cleanup

⚠️ Is this a breaking change?

• Yes, this change breaks existing functionality (explain in summary)
  No. This only fixes Windows compatibility for embedded template discovery and does not change generated artifacts or catalog contents.

🧪 Testing

• CI passed
• Manually tested (local/dev cluster)
• Unit tested
• Not tested (explain why below)

🔗 Related Issues / Tickets

Fixes: #502

✅ Checklist

• Code compiles and passes all tests
• Linting and style checks pass
• Comments added for complex logic
• Documentation updated (if applicable)

📎 Additional Context (optional)

Before:

After: