fix: correct infrahub-mcp Dockerfile and README (#7)

## 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

images/infrahub-mcp/Dockerfile

@@ -1,30 +1,37 @@
 FROM python:3.13-slim
 
-# Dépendances système pour uv et build éventuel de wheels
+# System dependencies for uv and potential wheel builds
 RUN apt-get update && \
     apt-get install -y --no-install-recommends git ca-certificates curl && \
     rm -rf /var/lib/apt/lists/*
 
-# Installer uv
+# Install uv
 COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
 
-# Cloner le repo MCP server upstream
-ARG INFRAHUB_MCP_VERSION=main
-RUN git clone --depth 1 --branch ${INFRAHUB_MCP_VERSION} \
-    https://github.com/opsmill/infrahub-mcp-server.git /app
+# Clone the upstream MCP server repository
+# Use INFRAHUB_MCP_VERSION to pin a specific tag/branch at build time
+# When left empty, the repo's default branch is used
+ARG INFRAHUB_MCP_VERSION=""
+RUN if [ -n "${INFRAHUB_MCP_VERSION}" ]; then \
+      git clone --depth 1 --branch "${INFRAHUB_MCP_VERSION}" \
+        https://github.com/opsmill/infrahub-mcp.git /app; \
+    else \
+      git clone --depth 1 \
+        https://github.com/opsmill/infrahub-mcp.git /app; \
+    fi
 
 WORKDIR /app
 
-# Installer les dépendances Python via uv
+# Install Python dependencies via uv
 RUN uv sync --frozen --no-dev
 
-# Variables d'environnement par défaut
+# Default environment variables
+# INFRAHUB_API_TOKEN should be passed at runtime (not baked into the image)
 ENV INFRAHUB_ADDRESS=http://localhost:8000
-ENV INFRAHUB_API_TOKEN=""
 ENV MCP_HOST=0.0.0.0
 ENV MCP_PORT=8001
 
 EXPOSE 8001
 
-# Lancer le serveur MCP en mode SSE (accessible via réseau)
+# Run the MCP server in SSE mode (network-accessible)
 ENTRYPOINT ["uv", "run", "fastmcp", "run", "src/infrahub_mcp/server.py:mcp", "--transport", "sse"]