Initial base distro with apko/Wolfi configs

Five minimal OCI image variants built with apko:
- base: ~5.5MB glibc runtime (wolfi-baselayout, libstdc++, ca-certs, tzdata)
- build: base + build tools (bash, git, curl, wget, unzip, xz)
- dotnet-runtime: base + ICU, OpenSSL, zlib for .NET runtime
- dotnet-sdk: build + ICU, OpenSSL, zlib for .NET SDK
- flutter: build variant configured for Flutter SDK

Includes melange package definitions for .NET 10 SDK/runtime and
Flutter SDK (for future use when building custom APKs).

CI/CD pipelines: publish on release, Scout CVE comparison on PRs,
weekly rebuild for Wolfi security patches.

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

examples/Dockerfile.flutter-web

@@ -0,0 +1,30 @@
+# Example: Flutter web build image using base-distro
+#
+# Usage in flutter-admin-console or other Flutter web projects:
+#   FROM svrnty/base-distro:flutter-latest AS build
+#   ... (install Flutter SDK, build web app) ...
+
+FROM svrnty/base-distro:flutter-latest AS build
+
+# Install Flutter SDK on top of the base
+USER root
+ARG FLUTTER_VERSION=3.38.9
+RUN curl -fsSL "https://storage.googleapis.com/flutter_infra_release/releases/stable/linux/flutter_linux_${FLUTTER_VERSION}-stable.tar.xz" \
+      -o /tmp/flutter.tar.xz && \
+    mkdir -p /opt && \
+    tar xf /tmp/flutter.tar.xz -C /opt && \
+    rm /tmp/flutter.tar.xz && \
+    git config --global --add safe.directory /opt/flutter && \
+    flutter config --enable-web \
+      --no-enable-android --no-enable-ios \
+      --no-enable-linux-desktop --no-enable-macos-desktop \
+      --no-enable-windows-desktop && \
+    flutter precache --web \
+      --no-android --no-ios --no-linux \
+      --no-macos --no-windows --no-fuchsia --no-universal && \
+    chown -R 65532:65532 /opt/flutter
+
+USER 65532
+WORKDIR /app
+COPY . .
+RUN flutter pub get && flutter build web --wasm --release