Bump Docker base images to node 22; mock firestore comment cleanup

Both Dockerfiles (root firebase-mode + docker/ caddy) bumped node:18-alpine
to node:22-alpine. better-sqlite3 v12 (from PR #6) requires node 20+; node 18
builds fail with node-gyp/python errors. openssl-legacy-provider flag kept
for react-scripts 5 compat.

.dockerignore: removed .env* exclusion so .env.local COPY works in firebase
image build.

mock firestore applyConstraints comment: offset handled by adapter (firebase.js
slices), mock never sees it — clarified dead-code reasoning.

Dockerfile

@@ -1,7 +1,7 @@
 # Dockerfile
 
 # Stage 1: Build the React application
-FROM node:18-alpine AS build
+FROM node:22-alpine AS build
 
 LABEL stage="build-local-testing"
 
@@ -48,4 +48,4 @@ COPY nginx-docker.conf /etc/nginx/conf.d/default.conf
 EXPOSE 80
 
 # Start Nginx when the container launches
-CMD ["nginx", "-g", "daemon off;"]
+CMD ["nginx", "-g", "daemon off;"]