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:

[tuunit]

@BittuBarnwal7479 thank you for the PR we didn't have the time yet to check it properly and check the rest of the codebase for similar issues related to windows support. We will try to get it into the next release in 2 weeks. Until then we recommend running/using the kubara cli inside WSL