chore: clean workspace deps and add CLAUDE.md

- Drop ipykernel from the root virtual dependency list; the
  workspace relies on its subpackages and uv lockfile to manage
  per-service dependencies.
- Refresh uv.lock to match the trimmed root dependency set.
- Add CLAUDE.md describing the workspace layout, common
  development and database commands, the Nginx/backend/runtime
  auth request flow, and the boundaries to keep in mind when
  changing services.

pyproject.toml

@@ -2,9 +2,7 @@
 name = "model-platform"
 version = "0.1.0"
 requires-python = ">=3.12"
-dependencies = [
-    "ipykernel>=7.3.0",
-]
+dependencies = []
 
 [tool.uv.workspace]
 members = [