fix(deploy): fix render-worker build context + migration 040 idempotency

- docker-compose.yml: change render-worker build context from ./render-worker
  to . (project root) so pyproject.toml is accessible; update dockerfile path
- render-worker/Dockerfile: update COPY paths for new build context;
  install Python 3.11 via deadsnakes PPA (Ubuntu 22.04 ships 3.10 which
  fails the >=3.11 requirement in pyproject.toml)
- 040_media_assets.py: rewrite upgrade() with raw idempotent SQL (CREATE TYPE
  inside DO $$ EXCEPTION WHEN duplicate_object $$; CREATE TABLE IF NOT EXISTS;
  CREATE INDEX IF NOT EXISTS) to handle pre-existing enum from partial runs

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

render-worker/Dockerfile

@@ -11,9 +11,17 @@ ENV PYOPENGL_PLATFORM=osmesa
 ENV VTK_DEFAULT_EGL=0
 
 # Runtime libraries for cadquery/OCC + Blender 5.x headless
+# Also installs Python 3.11 via deadsnakes PPA (Ubuntu 22.04 ships 3.10)
 RUN apt-get update && apt-get install -y --no-install-recommends \
+    software-properties-common gnupg gpg-agent \
+    && add-apt-repository ppa:deadsnakes/ppa -y \
+    && apt-get update && apt-get install -y --no-install-recommends \
+    python3.11 \
+    python3.11-dev \
+    python3.11-distutils \
     python3-pip \
     python3-dev \
+    curl \
     libpq-dev \
     gcc \
     libxrender1 \
@@ -40,21 +48,26 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /app
 
+# Use Python 3.11 as the default pip target
+RUN curl -sS https://bootstrap.pypa.io/get-pip.py | python3.11 \
+    && update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.11 1 \
+    && update-alternatives --install /usr/bin/pip3 pip3 /usr/local/bin/pip3.11 1
+
 # Install backend Python dependencies (includes celery, sqlalchemy, fastapi, etc.)
-COPY pyproject.toml .
+COPY backend/pyproject.toml .
 RUN pip3 install --no-cache-dir -e .
 
 # Install cadquery (heavy — installed after backend deps for better layer caching)
 RUN pip3 install --no-cache-dir "cadquery>=2.4.0"
 
 # Copy render scripts
-COPY scripts/ /render-scripts/
+COPY render-worker/scripts/ /render-scripts/
 
 # Version check script — fails fast if Blender < 5.0.1
-COPY check_version.py /check_version.py
+COPY render-worker/check_version.py /check_version.py
 
-# Copy app code (overridden by volume mount in docker-compose)
-COPY . .
+# Copy backend app code (overridden by volume mount in docker-compose)
+COPY backend/ .
 
 # Verify Blender version at build time if binary is available
 # (skipped during build since /opt/blender is a host mount)