Add OSS Scanner build environment and threat model

.oss-scanner/Dockerfile

@@ -0,0 +1,56 @@
+# Build environment for Anthropic's OSS Scanner (https://github.com/anthropics/oss-scanner).
+# The scanner builds this image with the repository root as the build context and then audits it without network
+# access, so everything needed to run the app and its test suite (PHP + Composer deps, Node deps + built frontend,
+# a local PostgreSQL) is installed here.
+#
+# Inside the finished image:
+#   .oss-scanner/start-postgres.sh    start the local PostgreSQL server (required for tests and the app)
+#   php artisan test                  run the PHPUnit suite
+#   php artisan serve                 run the app on http://127.0.0.1:8000 (after `php artisan migrate --seed`)
+
+FROM node:20-bookworm-slim AS node
+
+FROM php:8.3-cli-bookworm
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    COMPOSER_ALLOW_SUPERUSER=1 \
+    COMPOSER_NO_INTERACTION=1 \
+    TZ=UTC
+
+COPY --from=mlocati/php-extension-installer:2 /usr/bin/install-php-extensions /usr/local/bin/
+COPY --from=composer:2 /usr/bin/composer /usr/local/bin/composer
+COPY --from=node /usr/local/bin/node /usr/local/bin/node
+COPY --from=node /usr/local/lib/node_modules /usr/local/lib/node_modules
+RUN ln -s ../lib/node_modules/npm/bin/npm-cli.js /usr/local/bin/npm \
+    && ln -s ../lib/node_modules/npm/bin/npx-cli.js /usr/local/bin/npx
+
+# PostgreSQL 15 (Debian bookworm default) is the database solidtime runs and is tested against.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends git unzip curl ca-certificates postgresql postgresql-client \
+    && install-php-extensions pdo_pgsql pgsql intl gd zip bcmath exif pcntl sockets soap \
+    && rm -rf /var/lib/apt/lists/* \
+    && echo "memory_limit=2G" > "$PHP_INI_DIR/conf.d/99-oss-scanner.ini"
+
+# Database matching .env.ci: user root / password root, database laravel.
+RUN pg_ctlcluster 15 main start \
+    && runuser -u postgres -- psql -c "CREATE ROLE root WITH LOGIN SUPERUSER PASSWORD 'root';" \
+    && runuser -u postgres -- createdb -O root laravel \
+    && pg_ctlcluster 15 main stop
+
+# scanner contract: the checkout lives inside the image, at /src
+COPY . /src
+WORKDIR /src
+
+RUN composer install --prefer-dist \
+    && npm ci \
+    && npm run build
+
+RUN cp .env.ci .env \
+    && php artisan key:generate \
+    && php artisan passport:keys --force \
+    && chmod +x .oss-scanner/start-postgres.sh
+
+# Run the test suite so the image is known to work, but do not fail the build on test failures.
+RUN .oss-scanner/start-postgres.sh \
+    && (php artisan test || echo "WARNING: PHPUnit reported failures") \
+    && pg_ctlcluster 15 main stop