fix(client): drop stale COPY public in Dockerfile

docker build failed with "/public: not found" at the client stage. The
client tree has never contained a public/ directory (vite doesn't need one
for this project — index.html lives at the client root and vite.config.js
has no publicDir override). Remove the dead COPY line.

Verified: docker build -f client/Dockerfile client succeeds end-to-end.

client/Dockerfile

@@ -6,7 +6,6 @@ COPY package.json package-lock.json ./
 RUN npm ci
 
 COPY index.html vite.config.js ./
-COPY public public
 COPY src src
 RUN npm run build