Dockerize backend, frontend, and database into separate containers

- backend/Dockerfile: multi-stage Python build (builder + slim runtime)
- frontend/Dockerfile: multi-stage Node build + nginx:alpine serving
- frontend/nginx.conf: SPA routing + /api/ reverse proxy to backend
- docker-compose.yml: production compose with health checks and proper dependency ordering
- docker-compose.dev.yml: dev overrides with hot reload via volume mounts

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

backend/Dockerfile

@@ -0,0 +1,26 @@
+# ── Stage 1: dependency installation ─────────────────────────────────────────
+FROM python:3.12-slim AS builder
+
+WORKDIR /app
+
+RUN pip install --upgrade pip
+
+COPY pyproject.toml .
+RUN pip install --prefix=/install .
+
+# ── Stage 2: runtime ──────────────────────────────────────────────────────────
+FROM python:3.12-slim
+
+WORKDIR /app
+
+# Copy installed packages from builder
+COPY --from=builder /install /usr/local
+
+# Copy application source
+COPY app ./app
+COPY alembic ./alembic
+COPY alembic.ini .
+
+EXPOSE 8000
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]