chore: migrate to Nix flakes, remove Docker and legacy configs

Remove all Docker files, Vercel config, Verdaccio, and old CI workflow.
Standardize on nodejs_22 across devShell and nix build helpers.
Update CI to build all packages and push to Cachix on merge to develop.

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

apps/qrcampaign/Dockerfile

@@ -1,17 +0,0 @@
-FROM node:22-alpine AS deps
-WORKDIR /app
-COPY package.json package-lock.json ./
-RUN npm ci --prefer-offline --no-audit --no-fund
-
-FROM node:22-alpine AS builder
-WORKDIR /app
-COPY --from=deps /app/node_modules ./node_modules
-COPY . .
-ENV NX_DAEMON=false
-RUN npm run qrcampaign:build
-
-FROM nginx:alpine AS runner
-RUN rm -rf /usr/share/nginx/html/*
-COPY --from=builder /app/dist/apps/qrcampaign /usr/share/nginx/html
-EXPOSE 80
-CMD ["nginx", "-g", "daemon off;"]