fix(template): render v2alpha instance yaml before parsing

[zjy365]

Summary

• render template conditionals before parsing YAML in the v2alpha instance creation API
• keep the requested instance name by renaming the rendered Instance resource before apply
• add a regression test for conditional YAML that fails before rendering, matching the FastGPT failure mode

Testing

• pnpm --filter ./providers/template test:ci
• pnpm --filter ./providers/template build
• live probe: fetched fastgpt from https://template.gzg.sealos.run/api/getTemplateSource and verified local rendering succeeds with the patched renderer

Notes

• No public API schema changes. POST /api/v2alpha/templates/instances still accepts template/name/args and applies rendered YAML server-side.