Initialize git-contribution-graph project with Docker setup, environment configuration, and core functionality for merging contributions from GitHub, GitLab, and Gitea into an SVG heatmap.

Dockerfile

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+FROM php:8.3-cli-alpine AS base
+
+# Runtime dependencies
+RUN apk add --no-cache \
+    curl \
+    icu-libs \
+    libzip \
+    && docker-php-ext-install opcache
+
+# Composer
+COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
+
+WORKDIR /app
+
+# ── deps stage ────────────────────────────────────────────────────────────────
+FROM base AS deps
+COPY composer.json composer.lock* ./
+RUN composer install \
+        --no-dev \
+        --no-scripts \
+        --no-interaction \
+        --optimize-autoloader \
+        --prefer-dist
+
+# ── final stage ───────────────────────────────────────────────────────────────
+FROM base AS final
+
+COPY --from=deps /app/vendor /app/vendor
+COPY . .
+
+RUN mkdir -p var/cache var/log \
+    && chmod -R 777 var \
+    && composer dump-autoload --optimize --no-dev
+
+EXPOSE 8080
+
+ENV APP_ENV=prod \
+    APP_DEBUG=0
+
+# Symfony's built-in dev server via PHP — fine for a single-purpose container
+CMD ["php", "-S", "0.0.0.0:8080", "-t", "public", "public/index.php"]