refactor(docker): replace RUN_TESTS ARG with test stage

- Removed ARG RUN_TESTS and conditional if block
- Added dedicated 'test' stage for quality checks
- Usage: docker build --target test -t rentgen-test .
- Cleaner separation of concerns
- Updated README with new command

Dockerfile

@@ -4,9 +4,6 @@
 # Build stage
 FROM node:lts AS builder
 
-# Optional: run tests during build (typecheck + lint)
-ARG RUN_TESTS=false
-
 WORKDIR /app
 
 # Copy package files for dependency installation (better layer caching)
@@ -24,13 +21,9 @@ RUN npm run build
 # Create the package
 RUN npm run create-package
 
-# Optional: run quality checks
-RUN if [ "$RUN_TESTS" = "true" ]; then \
-        echo "Running TypeScript type checking..."; \
-        npm run typecheck; \
-        echo "Running web-ext lint..."; \
-        npm run lint; \
-    fi
+# Test stage - for running quality checks
+FROM builder AS test
+RUN npm run typecheck && npm run lint
 
 # Artifacts stage - only contains the built artifacts (for --output)
 FROM scratch AS artifacts

README.md

@@ -54,7 +54,7 @@ This will build the extension and extract the `.zip` file to the `artifacts/` di
 ### Build with tests (typecheck + lint)
 
 ```bash
-docker build --build-arg RUN_TESTS=true -t rentgen .
+docker build --target test -t rentgen-test .
 ```
 
 ### Traditional build (creates full development environment)