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.

docker/Dockerfile

@@ -2,7 +2,7 @@
 # docker/Dockerfile --- single container: caddy (front) + node (back).
 # Build context = repo root.
 # ---- build stage: frontend + install backend deps ----
-FROM node:18-alpine AS build
+FROM node:22-alpine AS build
 WORKDIR /app
 
 COPY package*.json ./
@@ -30,7 +30,7 @@ RUN cd server && npm rebuild better-sqlite3
 
 
 # ---- runtime stage: caddy + node ----
-FROM node:18-alpine
+FROM node:22-alpine
 RUN apk add --no-cache caddy
 
 WORKDIR /app