chore: scaffold the Serverpod 4 build

Deviations from a stock `serverpod create`:
- Dropped Flutter web support, for two reasons:
  - Appflowy editor had issues in the past, potentially related to the
    Flutter-Web IME bridge. Upstream has also open bugs in relation to
that:
    - AppFlowy-IO/appflowy-editor#1029 [Bug][Web] Unwanted space on click
       and overall space bugs (open)
    - AppFlowy-IO/appflowy-editor#782 [Bug] Editor auto-scrolling when
       pressing space too quickly if placed inside a scrollable (open)
  - Offline-first is a required feature. serverpod_offline_sync's SQLite
    support in browsers, maybe via sqlite3.wasm + OPFS, is not
documented.
- SDK constraints raised to ^3.13.0, instead of ^3.12.2, so enjoy the
  newest language features.
- Pinned to Flutter 3.47.4 via FVM.

Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_server/Dockerfile

@@ -0,0 +1,58 @@
+# Build from the project root with:
+# docker build -f halkyon_learn_server/Dockerfile .
+
+# Build stage
+FROM dart:3.12.2 AS build
+
+# Create a minimal workspace that preserves locked server dependency versions.
+WORKDIR /app
+COPY pubspec.lock .
+COPY halkyon_learn_server halkyon_learn_server
+RUN printf '%s\n' \
+  'name: _' \
+  'environment:' \
+  '  sdk: ^3.12.2' \
+  'workspace:' \
+  '  - halkyon_learn_server' \
+  > pubspec.yaml
+RUN dart pub get
+
+# Compile the server executable.
+WORKDIR /app/halkyon_learn_server
+RUN dart build cli --target bin/main.dart --output build
+RUN mv build/bundle/bin/main build/bundle/bin/server
+
+# Add a fallback for the copy of possibly missing directories.
+RUN mkdir -p config web migrations
+
+# Final stage
+FROM alpine:latest
+WORKDIR /app
+
+# Environment variables
+ENV runmode=production
+ENV serverid=default
+ENV logging=normal
+ENV role=monolith
+
+# Copy runtime dependencies
+COPY --from=build /runtime/ /
+
+# Copy compiled server executable and native libraries
+COPY --from=build /app/halkyon_learn_server/build/bundle/ ./
+
+# Copy configuration files and resources
+COPY --from=build /app/halkyon_learn_server/config/ config/
+COPY --from=build /app/halkyon_learn_server/web/ web/
+COPY --from=build /app/halkyon_learn_server/migrations/ migrations/
+
+# This file is required to enable the endpoint log filter in Insights.
+COPY --from=build /app/halkyon_learn_server/lib/src/generated/protocol.yaml lib/src/generated/protocol.yaml
+
+# Expose ports
+EXPOSE 8080
+EXPOSE 8081
+EXPOSE 8082
+
+# Define the entrypoint command
+ENTRYPOINT ./bin/server --mode=$runmode --server-id=$serverid --logging=$logging --role=$role