fix: add build-system config to workspace root pyproject.toml

Setuptools auto-discovery found multiple top-level directories (site,
images, agents, topics, research, packages) and refused to build.

Added [build-system] and [tool.setuptools] py-modules = [] to declare
the workspace root has no packages of its own. The installable packages
are in packages/studyctl and packages/agent-session-tools.

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

Author: taylaand

pyproject.toml

@@ -24,6 +24,13 @@ dev = [
     "pre-commit>=4.0",
 ]
 
+[build-system]
+requires = ["setuptools>=75"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools]
+py-modules = []  # Workspace root — no packages to install here
+
 [tool.uv.workspace]
 members = ["packages/*"]