fix: collapse python3 -c to single line to fix dockerfile parse error

Dockerfile

@@ -26,7 +26,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 # ---- Prepare Django Python Backend ----
 COPY backend/requirements.txt ./backend/requirements.txt
-# Upgrade pip and install requirements + gunicorn directly in container
+# Upgrade pip and install requirements + gunicorn + huggingface_hub for model download
 RUN pip install --no-cache-dir --upgrade pip setuptools wheel \
     && pip install --no-cache-dir -r ./backend/requirements.txt \
     && pip install --no-cache-dir gunicorn huggingface_hub
@@ -34,19 +34,12 @@ RUN pip install --no-cache-dir --upgrade pip setuptools wheel \
 COPY backend/ ./backend/
 
 # ---- Download ONNX model from Hugging Face Hub ----
-# The model is too large for git — it lives in a dedicated HF model repo.
-RUN python3 -c "
-from huggingface_hub import hf_hub_download
-import shutil, pathlib
-dst = pathlib.Path('/app/backend/model')
-dst.mkdir(parents=True, exist_ok=True)
-path = hf_hub_download(repo_id='${HF_MODEL_REPO}', filename='dermavision.onnx', local_dir=str(dst))
-print(f'Model downloaded to {path}')
-"
+# Single-line form required — Dockerfile parser breaks on multi-line python3 -c "..." blocks
+RUN python3 -c "import pathlib, huggingface_hub; dst=pathlib.Path('/app/backend/model'); dst.mkdir(parents=True, exist_ok=True); huggingface_hub.hf_hub_download(repo_id='${HF_MODEL_REPO}', filename='dermavision.onnx', local_dir=str(dst)); print('Model downloaded OK')"
 
 # ---- Prepare Node.js & React Frontend ----
 COPY package*.json ./
-# Force installation of devDependencies (Vite, esbuild, typescript) for building, even if NODE_ENV=production
+# Force installation of devDependencies (Vite, esbuild, typescript) for building
 RUN npm ci --include=dev
 
 COPY . .