## What changed
Fixes the build failure caused by wrong upstream repo URL and missing default branch.
### Dockerfile
- **Repo URL**: `opsmill/infrahub-mcp` (was `opsmill/infrahub-mcp-server`)
- **Default branch**: clone without `--branch` when `INFRAHUB_MCP_VERSION` is unset, so the upstream default branch is used automatically
- **Secrets warning**: removed `ENV INFRAHUB_API_TOKEN=""` — the token should be passed at runtime via `-e`, not baked into the image
- **Comments**: rewritten in English
### README
- Fixed upstream repo link
- Clarified that `INFRAHUB_API_TOKEN` is required at runtime
Reviewed-on: #7
