Switch final stage to node:20-slim for better-sqlite3 compatibility

Alpine's musl libc causes repeated npm ci failures for better-sqlite3's
native module compilation. node:20-slim (Debian) uses glibc and compiles
reliably. Client builder stage stays Alpine since it has no native deps.

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

Dockerfile

@@ -16,21 +16,21 @@ COPY client/public ./public
 # Build React app
 RUN npm run build
 
-# Final stage - Node.js server
-FROM node:20-alpine
+# Final stage - Node.js server (slim Debian for glibc native module compatibility)
+FROM node:20-slim
 
 WORKDIR /app
 
-# Install dumb-init for proper signal handling
-RUN apk add --no-cache dumb-init
+# Install dumb-init and build tools needed by better-sqlite3
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    dumb-init python3 make g++ \
+    && rm -rf /var/lib/apt/lists/*
 
 # Copy server package files
 COPY package*.json ./
 
-# Install build tools for native modules (better-sqlite3), then install deps
-RUN apk add --no-cache python3 build-base linux-headers && \
-    npm ci --omit=dev && \
-    apk del python3 build-base linux-headers
+# Install production dependencies only
+RUN npm ci --omit=dev
 
 # Copy server code
 COPY server ./server
@@ -38,12 +38,11 @@ COPY server ./server
 # Copy built React client from builder stage
 COPY --from=client-builder /app/client/build ./client/build
 
-# Create data directory and set permissions
-RUN mkdir -p /app/data && chown -R 1001:1001 /app
-
-# Create non-root user
-RUN addgroup -g 1001 -S nodejs && \
-    adduser -S nodejs -u 1001
+# Create non-root user and data directory
+RUN groupadd -g 1001 nodejs && \
+    useradd -u 1001 -g nodejs nodejs && \
+    mkdir -p /app/data && \
+    chown -R nodejs:nodejs /app
 
 USER nodejs