fix: lock against public PyPI so the image builds outside the workstation

uv.lock was originally resolved with the workstation's globally-configured
dexterenergy private artifact registry as the default index, baking that
URL into every `source = { registry = ... }` entry. Inside Docker that
401s.

- pyproject.toml: declare https://pypi.org/simple as the project's
  default uv index (overrideable, but pins intent)
- uv.lock: regenerated with UV_DEFAULT_INDEX=https://pypi.org/simple and
  no UV_INDEX so every source now points at public PyPI

Reproduce: `UV_DEFAULT_INDEX=https://pypi.org/simple UV_INDEX= uv lock`

pyproject.toml

@@ -8,3 +8,11 @@ dependencies = [
     "uvicorn[standard]>=0.32",
     "httpx>=0.27",
 ]
+
+# Pin to public PyPI explicitly. Without this, uv inherits whichever index
+# the workstation has configured globally — e.g. the dexterenergy private
+# artifact registry — and bakes it into uv.lock, which 401s inside Docker.
+[[tool.uv.index]]
+name = "pypi"
+url = "https://pypi.org/simple"
+default = true