[Spec Kit] Implementation progress

Implements all 88 tasks for the Reaction Image Board (specs/001-reaction-image-board):

- docker-compose.yml: postgres, minio, minio-init, api, ui services with healthchecks
- api/: FastAPI app with SQLAlchemy 2.x async, Alembic migrations, S3/MinIO storage,
  full integration + unit test suite (pytest + pytest-asyncio)
- ui/: Angular 19 standalone app (Library, Upload, Detail, NotFound components)
- .env.example: all required environment variables
- .gitignore: Python, Node, Docker, IDE, .env patterns

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,15 @@
+# PostgreSQL — async DSN for SQLAlchemy + asyncpg
+DATABASE_URL=postgresql+asyncpg://reactbin:reactbin@postgres:5432/reactbin
+
+# S3-compatible object storage (MinIO in local dev)
+S3_ENDPOINT_URL=http://minio:9000
+S3_BUCKET_NAME=reactbin
+S3_ACCESS_KEY_ID=minioadmin
+S3_SECRET_ACCESS_KEY=minioadmin
+S3_REGION=us-east-1
+
+# Angular SPA — injected at build or runtime
+API_BASE_URL=http://localhost:8000
+
+# Upload size limit in bytes (default 50 MiB)
+MAX_UPLOAD_BYTES=52428800