fix: declare httpx as direct dependency

docs/changelogs/0.8.x.md

@@ -22,6 +22,10 @@ All notable changes in the **0.8.x** release series are documented here.
   and `--version`, keep the run itself on stdout, return benchmark-safe exit
   codes, and preserve API and transport error text on stderr.
 
+### Fixed
+- Declare `httpx` as a direct runtime dependency so clean and containerized
+  installations do not rely on `anthropic` to install it transitively.
+
 <!--
 When cutting a release, copy the relevant items from [Unreleased] into a new
 version section above it, e.g.:

pyproject.toml

@@ -15,6 +15,7 @@ classifiers = [
 ]
 dependencies = [
     "anthropic>=0.112.0",
+    "httpx>=0.25.0",
 ]
 
 [project.urls]