upgrade to Node 24 LTS + @types/node v24

- Dockerfile: node:20-slim → node:24-slim (all 3 stages)
- @types/node: ^20.12.12 → ^24.0.0
- Fixes EBADENGINE warning (@discordjs/voice requires Node >=22)
- Brings npm 11 automatically
- Node 24 LTS supported until April 2028

Dockerfile

@@ -1,7 +1,7 @@
 # Multi-stage build: Frontend (Vite) + Backend (Express + discord.js)
 
 # --- Build frontend (npm) ---
-FROM node:20-slim AS web-build
+FROM node:24-slim AS web-build
 WORKDIR /app/web
 COPY web/package*.json ./
 RUN npm install --no-audit --no-fund
@@ -14,7 +14,7 @@ ENV VITE_APP_VERSION=$VITE_APP_VERSION
 RUN npm run build
 
 # --- Build server (npm) ---
-FROM node:20-slim AS server-build
+FROM node:24-slim AS server-build
 WORKDIR /app/server
 RUN apt-get update && apt-get install -y python3 make g++ && rm -rf /var/lib/apt/lists/*
 COPY server/package*.json ./
@@ -25,7 +25,7 @@ RUN npm run build
 RUN rm -rf node_modules && npm install --omit=dev --no-audit --no-fund
 
 # --- Runtime image ---
-FROM node:20-slim AS runtime
+FROM node:24-slim AS runtime
 WORKDIR /app
 ENV NODE_ENV=production
 ENV PORT=8080