fix(build): ensure fresh Flutter build on each deploy

- Add flutter clean before build to prevent stale cached artifacts
- Add VERSION build arg for explicit cache busting
- Reorder build steps: clean → pub get → build_runner → health.json → build
- Replace deprecated dart:html with package:web in iframe_view_web.dart
- Add lint ignore to generate_health_json.dart

Fixes issue where Docker layer caching kept old main.dart.js
while regenerating health.json with new version number.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -3,16 +3,24 @@ FROM ghcr.io/cirruslabs/flutter:stable AS builder
 
 WORKDIR /app
 
-# Copy dependency files first for better caching
-COPY pubspec.yaml ./
+# VERSION arg busts cache when version changes in pubspec.yaml
+# Extract version: docker build --build-arg VERSION=$(grep '^version:' pubspec.yaml | cut -d' ' -f2) .
+ARG VERSION=0.0.0
+RUN echo "Building version: $VERSION"
 
-# Get dependencies (generates pubspec.lock)
+# Copy dependency files first for better caching
+COPY pubspec.yaml pubspec.lock* ./
+
+# Get dependencies
 RUN flutter pub get
 
 # Copy the rest of the application
 COPY . .
 
-# Generate code with build_runner
+# Clean any cached build artifacts to ensure fresh build
+RUN flutter clean && flutter pub get
+
+# Generate code with build_runner (after clean for fresh generation)
 RUN dart run build_runner build --delete-conflicting-outputs
 
 # Generate health.json with version info