Initial implementation of duplicate finder

Full project per spec: FastAPI backend, 4-method duplicate detection
(SHA-256, phash, EXIF, filesize), Google Takeout pre-processor,
4 scan modes, and dark-theme vanilla JS gallery frontend.

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

Dockerfile

@@ -0,0 +1,15 @@
+FROM python:3.12-slim
+
+RUN apt-get update && apt-get install -y \
+    libheif-dev libjpeg-dev libpng-dev libtiff-dev libwebp-dev exiftool \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+COPY app/ /app/
+COPY templates/ /app/templates/
+RUN mkdir -p /data /photos /app/static
+
+EXPOSE 8000
+CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000", "--workers", "1"]