Simplify Dockerfile.browser to 2-stage build (#969)

Consolidates the browser mode Docker build from 3 stages to 2 by
removing the redundant intermediate `deps` stage and cleaning dev
dependencies in-place after build.

## Changes

- **Stage 1 (builder)**: Install all deps → build → remove dev deps with
`yarn install --production`
- **Stage 2 (production)**: Copy built artifacts and production
node_modules from builder (previously split across builder + deps
stages)

**Before:**
```dockerfile
# Stage 1: Build
RUN yarn install --frozen-lockfile
RUN yarn build:server

# Stage 2: Production dependencies
COPY --from=builder /build/package.json /build/yarn.lock ./
RUN yarn install --production --frozen-lockfile

# Stage 3: Production
COPY --from=builder /build/dist ./dist
COPY --from=deps /deps/node_modules ./node_modules
```

**After:**
```dockerfile
# Stage 1: Build and prepare production dependencies
RUN yarn install --frozen-lockfile
RUN yarn build:server
RUN yarn install --production --frozen-lockfile

# Stage 2: Production
COPY --from=builder /build/dist ./dist
COPY --from=builder /build/node_modules ./node_modules
```

No functional changes to final image; eliminates redundant package
resolution and copying.

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<details>

<summary>Original prompt</summary>

> simplify the Dockerfile browser build, install dependencies and build
in the first stage, after the build remove the dev dependency


</details>



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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: thomasnordquist <7721625+thomasnordquist@users.noreply.github.com>

Dockerfile.browser

@@ -1,5 +1,5 @@
 # Multi-stage build for MQTT Explorer Browser Mode
-# Stage 1: Build
+# Stage 1: Build and prepare production dependencies
 FROM node:24-alpine AS builder
 
 WORKDIR /build
@@ -18,20 +18,12 @@ RUN yarn install --frozen-lockfile --network-timeout 100000
 # Build the application (compiles TypeScript and webpack bundles)
 RUN yarn build:server
 
-# Stage 2: Production dependencies
+# Remove dev dependencies, keeping only production dependencies
-FROM node:24-alpine AS deps
-
-WORKDIR /deps
-
-# Copy only package files
-COPY --from=builder /build/package.json /build/yarn.lock ./
-
-# Install ONLY production dependencies
 RUN yarn install --production --frozen-lockfile --network-timeout 100000 && \
     yarn cache clean && \
     rm -rf /tmp/*
 
-# Stage 3: Production
+# Stage 2: Production
 FROM node:24-alpine
 
 # Install dumb-init in a single layer
@@ -50,8 +42,8 @@ COPY --from=builder --chown=mqttexplorer:mqttexplorer /build/dist ./dist
 COPY --from=builder --chown=mqttexplorer:mqttexplorer /build/app/build ./app/build
 COPY --from=builder --chown=mqttexplorer:mqttexplorer /build/app/index.html ./app/
 
-# Copy runtime node_modules (minimal set)
+# Copy runtime node_modules (production dependencies only)
-COPY --from=deps --chown=mqttexplorer:mqttexplorer /deps/node_modules ./node_modules
+COPY --from=builder --chown=mqttexplorer:mqttexplorer /build/node_modules ./node_modules
 
 # Copy package.json for version info (needed by server)
 COPY --from=builder --chown=mqttexplorer:mqttexplorer /build/package.json ./