Set git default branch to main in Docker image

Prevents master/main mismatch when pushing new case repos to Gitea.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -5,7 +5,8 @@ WORKDIR /app
 # System deps for PyMuPDF and document processing
 RUN apt-get update && apt-get install -y --no-install-recommends \
     gcc libmupdf-dev libfreetype6-dev libharfbuzz-dev libjpeg62-turbo-dev \
-    libopenjp2-7-dev curl git && rm -rf /var/lib/apt/lists/*
+    libopenjp2-7-dev curl git && rm -rf /var/lib/apt/lists/* && \
+    git config --global init.defaultBranch main
 
 # Copy Ezer Mishpati MCP server source
 COPY mcp-server/pyproject.toml /app/mcp-server/pyproject.toml