Add Docker Compose setup for local runs

PHP 8.3 + Apache image serving public/ on port 8080, with pdo_sqlite and
mbstring built in. The container entrypoint applies migrations as www-data
before starting Apache; the SQLite database and generated JWT signing key
persist in a named "storage" volume. `docker compose up -d` is now the
primary way to run the project without a local PHP toolchain.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker/apache.conf

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+<VirtualHost *:80>
+    DocumentRoot /var/www/html/public
+
+    <Directory /var/www/html/public>
+        Options -Indexes +FollowSymLinks
+        AllowOverride All
+        Require all granted
+        DirectoryIndex index.php
+    </Directory>
+
+    ErrorLog ${APACHE_LOG_DIR}/error.log
+    CustomLog ${APACHE_LOG_DIR}/access.log combined
+</VirtualHost>

docker/entrypoint.sh

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+#!/bin/sh
+set -e
+
+# The storage directory may be a freshly created named volume; make sure it
+# exists and is writable by the web-server user.
+mkdir -p storage
+chown -R www-data:www-data storage
+
+# Apply pending migrations as www-data so the SQLite file it creates stays
+# writable by Apache.
+su -s /bin/sh -c 'php bin/migrate.php' www-data
+
+exec docker-php-entrypoint "$@"