Add .dockerignore files and increase Node memory limit

Prevents node_modules/dist from polluting Docker build context.
Sets NODE_OPTIONS max-old-space-size=4096 for Vite builds on
memory-constrained servers.

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

frontend/.dockerignore

@@ -0,0 +1,7 @@
+node_modules
+dist
+.git
+.gitignore
+*.md
+.vscode
+.env*

frontend/Dockerfile

@@ -1,5 +1,6 @@
 FROM node:22 AS build
 WORKDIR /app
+ENV NODE_OPTIONS=--max-old-space-size=4096
 COPY package*.json ./
 RUN npm ci
 COPY . .