Remove npm from Dockerfile - Phoenix uses esbuild/tailwind

Modern Phoenix apps don't use npm. They use standalone esbuild and
tailwind binaries. Removed npm installation and npm ci/deploy commands.
The mix assets.deploy task handles all asset compilation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Dockerfile

@@ -2,7 +2,7 @@
 FROM elixir:1.17-alpine AS build
 
 # Install build dependencies
-RUN apk add --no-cache build-base git nodejs npm
+RUN apk add --no-cache build-base git
 
 # Prepare build dir
 WORKDIR /app
@@ -26,8 +26,6 @@ COPY lib lib
 COPY assets assets
 
 # Compile assets
-RUN npm ci --prefix ./assets
-RUN npm run deploy --prefix ./assets
 RUN mix assets.deploy
 
 # Compile the project