Add Summit Stride 5K training tracker at /running

Node/Express backend with SQLite storage, WebAuthn passkey auth,
and React frontend built via Vite. Caddy routes /running/* via
handle_path labels on docker-compose.

apps/running/Dockerfile

@@ -0,0 +1,18 @@
+# Stage 1: Build frontend
+FROM node:20-alpine AS builder
+WORKDIR /app/src
+COPY src/package.json ./
+RUN npm install
+COPY src/ ./
+RUN npm run build
+
+# Stage 2: Production server
+FROM node:20-alpine
+WORKDIR /app
+COPY package.json ./
+RUN npm install --omit=dev
+COPY server.js ./
+COPY --from=builder /app/src/dist ./public
+RUN mkdir -p /app/data
+EXPOSE 8080
+CMD ["node", "server.js"]