fix: simplify Dockerfile by removing user creation and ownership commands

flutter/Dockerfile

@@ -3,15 +3,10 @@ FROM ghcr.io/cirruslabs/flutter:stable AS builder
 
 WORKDIR /app
 
-RUN useradd -m -u 10001 flutteruser
-RUN chown -R flutteruser:flutteruser /sdks/flutter/bin/cache
-
-COPY --chown=flutteruser:flutteruser pubspec.yaml pubspec.lock* ./
-USER flutteruser
-RUN git config --global --add safe.directory /sdks/flutter
+COPY pubspec.yaml pubspec.lock* ./
 RUN flutter pub get
 
-COPY --chown=flutteruser:flutteruser . .
+COPY . .
 
 # Inject API base URL at build time via --dart-define.
 # Default to same-origin /api to avoid mixed-content in HTTPS deployments.