chore: update Docker and compose files for PaddleOCR engine (refs #119)

- Replace libtesseract-dev with libgomp1 (OpenMP for PaddlePaddle)
- Pre-download PP-OCRv4 models during Docker build
- Add OCR engine env vars to all compose files (base, staging, prod)
- Add optional Google Vision secret mount (commented, enable on demand)
- Create google-vision-key.json.example placeholder

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

ocr/Dockerfile

@@ -1,5 +1,9 @@
 # Production Dockerfile for MotoVaultPro OCR Service
 # Uses mirrored base images from Gitea Package Registry
+#
+# Primary engine: PaddleOCR PP-OCRv4 (models baked into image)
+# Backward compat: Tesseract 5.x (optional, via TesseractEngine)
+# Cloud fallback: Google Vision (optional, requires API key at runtime)
 
 # Build argument for registry (defaults to Gitea mirrors, falls back to Docker Hub)
 ARG REGISTRY_MIRRORS=git.motovaultpro.com/egullickson/mirrors
@@ -7,10 +11,16 @@ ARG REGISTRY_MIRRORS=git.motovaultpro.com/egullickson/mirrors
 FROM ${REGISTRY_MIRRORS}/python:3.13-slim
 
 # System dependencies
+# - tesseract-ocr/eng: Backward-compatible OCR engine (used by TesseractEngine)
+# - libgomp1: OpenMP runtime required by PaddlePaddle
+# - libheif1/libheif-dev: HEIF image support (iPhone photos)
+# - libglib2.0-0: GLib shared library (OpenCV dependency)
+# - libmagic1: File type detection
+# - curl: Health check endpoint
 RUN apt-get update && apt-get install -y --no-install-recommends \
     tesseract-ocr \
     tesseract-ocr-eng \
-    libtesseract-dev \
+    libgomp1 \
     libheif1 \
     libheif-dev \
     libglib2.0-0 \
@@ -23,6 +33,12 @@ WORKDIR /app
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
+# Pre-download PaddleOCR PP-OCRv4 models during build (not at runtime).
+# Models are baked into the image so container starts are fast and
+# no network access is needed at runtime for model download.
+RUN python -c "from paddleocr import PaddleOCR; PaddleOCR(use_angle_cls=True, lang='en', use_gpu=False, show_log=False)" \
+    && echo "PaddleOCR PP-OCRv4 models downloaded and verified"
+
 COPY . .
 
 EXPOSE 8000