fix(docker): upgrade to Node.js 22 for ESM require() support

nanoid v5 and express-rate-limit v8 are ESM-only but esbuild outputs
CJS require() calls. Node.js 20 crashes with ERR_REQUIRE_ESM;
Node.js 22.12+ supports require() of ESM modules natively.

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

Author: junzero741

apps/backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:20-slim AS builder
+FROM node:22-slim AS builder
 
 WORKDIR /app
 
@@ -27,7 +27,7 @@ RUN pnpm nx build backend
 RUN pnpm nx prune backend
 
 # --- Production stage ---
-FROM node:20-slim
+FROM node:22-slim
 
 RUN apt-get update -y && apt-get install -y openssl && rm -rf /var/lib/apt/lists/*