Add complete web interface with Next.js frontend

- Initialize Next.js 14 app with TypeScript and Tailwind CSS
- Create authentication flows (login, register, OAuth)
- Build dashboard with overview statistics
- Implement mail accounts management (list, add, edit, delete)
- Add auto-detect and test connection features
- Create responsive layout with sidebar navigation
- Configure Docker deployment for frontend
- Update docker-compose.new.yml with frontend service
- Add comprehensive web interface documentation

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/Dockerfile

@@ -0,0 +1,51 @@
+# Frontend Dockerfile for Next.js
+FROM node:18-alpine AS base
+
+# Install dependencies only when needed
+FROM base AS deps
+RUN apk add --no-cache libc6-compat
+WORKDIR /app
+
+# Copy package files
+COPY package.json package-lock.json* ./
+RUN npm ci
+
+# Rebuild the source code only when needed
+FROM base AS builder
+WORKDIR /app
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+# Set environment variable for build
+ENV NEXT_TELEMETRY_DISABLED=1
+
+RUN npm run build
+
+# Production image, copy all the files and run next
+FROM base AS runner
+WORKDIR /app
+
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
+
+RUN addgroup --system --gid 1001 nodejs
+RUN adduser --system --uid 1001 nextjs
+
+COPY --from=builder /app/public ./public
+
+# Set the correct permission for prerender cache
+RUN mkdir .next
+RUN chown nextjs:nodejs .next
+
+# Automatically leverage output traces to reduce image size
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
+
+USER nextjs
+
+EXPOSE 3000
+
+ENV PORT=3000
+ENV HOSTNAME="0.0.0.0"
+
+CMD ["node", "server.js"]