chore: update pyproject.toml to include package configuration for setuptools

- Added package configuration for the 'app' module in `pyproject.toml`.
- Included `py.typed` in package data to support type checking.

backend/pyproject.toml

@@ -2,7 +2,6 @@
 name = "webref-backend"
 version = "1.0.0"
 description = "Reference Board Viewer - Backend API"
-readme = "README.md"
 requires-python = ">=3.12"
 dependencies = [
     "fastapi>=0.115.0",
@@ -32,6 +31,12 @@ dev = [
 requires = ["setuptools>=61.0"]
 build-backend = "setuptools.build_meta"
 
+[tool.setuptools]
+packages = ["app"]
+
+[tool.setuptools.package-data]
+app = ["py.typed"]
+
 [tool.ruff]
 # Exclude common paths
 exclude = [