[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>

api/tests/unit/test_validation.py

@@ -0,0 +1,34 @@
+import pytest
+from app.validation import validate_mime_type, validate_file_size, MimeTypeError, FileSizeError
+
+ACCEPTED_TYPES = ["image/jpeg", "image/png", "image/gif", "image/webp"]
+REJECTED_TYPES = ["application/pdf", "video/mp4", "text/plain", "application/octet-stream"]
+
+
+@pytest.mark.parametrize("mime_type", ACCEPTED_TYPES)
+def test_mime_type_accepts_images(mime_type):
+    validate_mime_type(mime_type)  # should not raise
+
+
+@pytest.mark.parametrize("mime_type", REJECTED_TYPES)
+def test_mime_type_rejects_non_images(mime_type):
+    with pytest.raises(MimeTypeError):
+        validate_mime_type(mime_type)
+
+
+def test_file_size_accepts_within_limit():
+    validate_file_size(1024, max_bytes=52_428_800)  # should not raise
+
+
+def test_file_size_accepts_exact_limit():
+    validate_file_size(52_428_800, max_bytes=52_428_800)  # should not raise
+
+
+def test_file_size_rejects_over_limit():
+    with pytest.raises(FileSizeError):
+        validate_file_size(52_428_801, max_bytes=52_428_800)
+
+
+def test_file_size_rejects_zero():
+    with pytest.raises(FileSizeError):
+        validate_file_size(0, max_bytes=52_428_800)