feat(dwg): switch to ODA File Converter (libredwg too unstable)

ODA File Converter handles all DWG versions reliably.
Uses xvfb for headless Qt operation in Docker.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dwg2dxf-api/Dockerfile

@@ -1,42 +1,27 @@
-FROM ubuntu:24.04 AS builder
-
-RUN apt-get update && \
-    apt-get install -y --no-install-recommends \
-        build-essential autoconf automake libtool pkg-config \
-        wget ca-certificates && \
-    rm -rf /var/lib/apt/lists/*
-
-# Build libredwg from source (not available in apt repos)
-ARG LIBREDWG_VERSION=0.13.3
-RUN wget -q "https://github.com/LibreDWG/libredwg/releases/download/${LIBREDWG_VERSION}/libredwg-${LIBREDWG_VERSION}.tar.xz" && \
-    tar xf "libredwg-${LIBREDWG_VERSION}.tar.xz" && \
-    cd "libredwg-${LIBREDWG_VERSION}" && \
-    ./configure --prefix=/usr/local --disable-static --disable-docs && \
-    make -j"$(nproc)" && \
-    make install
-
-# ---
-
 FROM ubuntu:24.04
 
-# Copy only the built binaries and libraries
-COPY --from=builder /usr/local/bin/dwg2dxf /usr/local/bin/
-COPY --from=builder /usr/local/lib/libredwg* /usr/local/lib/
-
-RUN ldconfig && \
-    apt-get update && \
-    apt-get install -y --no-install-recommends python3 python3-pip && \
+# ODA File Converter needs Qt libs + virtual framebuffer for headless mode
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        python3 python3-pip wget ca-certificates \
+        xvfb libxcb-xinerama0 libxcb-icccm4 libxcb-image0 \
+        libxcb-keysyms1 libxcb-randr0 libxcb-render-util0 \
+        libxcb-shape0 libxcb-xkb1 libxkbcommon0 libxkbcommon-x11-0 \
+        libglib2.0-0 libgl1 libfontconfig1 libfreetype6 && \
     pip3 install --no-cache-dir --break-system-packages flask && \
     apt-get purge -y python3-pip && \
     apt-get autoremove -y && \
     rm -rf /var/lib/apt/lists/*
 
+# Download and install ODA File Converter
+RUN wget -q "https://download.opendesign.com/guestfiles/Demo/ODAFileConverter_QT6_lnxX64_8.3dll_25.12.deb" \
+        -O /tmp/oda.deb && \
+    dpkg -i /tmp/oda.deb || apt-get install -f -y && \
+    rm /tmp/oda.deb
+
 WORKDIR /app
 COPY app.py .
 
-RUN useradd --system --no-create-home converter
-USER converter
-
 EXPOSE 5001
 
 HEALTHCHECK --interval=30s --timeout=5s --retries=3 \