Fix git not found error crashing document uploads in container

Install git in Docker image and wrap all subprocess git calls in
try/except so a missing or failing git binary never kills an upload
that already succeeded.

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

Dockerfile

@@ -34,7 +34,7 @@ WORKDIR /app
 
 # Install Node.js 20.x
 RUN apt-get update && apt-get install -y --no-install-recommends \
-      curl ca-certificates \
+      curl ca-certificates git \
  && curl -fsSL https://deb.nodesource.com/setup_20.x | bash - \
  && apt-get install -y --no-install-recommends nodejs \
  && rm -rf /var/lib/apt/lists/*