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>

.dockerignore

@@ -0,0 +1,10 @@
+.git
+.gitignore
+.dockerignore
+vendor
+storage
+.env
+.phpunit.cache
+.phpunit.result.cache
+docs
+README.md