chore: drop unused dependencies

Runtime deps (``[project] dependencies``):
- ``litellm[proxy]>=1.83.0`` — ``openai-agents[litellm]==0.14.6``
  already pulls litellm as a transitive (currently 1.83.7), and we
  only use ``litellm.completion()``, not the proxy server extras.
- ``defusedxml>=0.7.1`` — leftover from the XML tool-call era; zero
  imports remain.

Sandbox deps (``[project.optional-dependencies] sandbox``):
- ``pyte>=0.8.1`` — zero imports.
- ``numpydoc>=1.8.0`` — zero imports.

Optional groups:
- Drop the entire ``vertex`` group (``google-cloud-aiplatform``);
  routing goes through litellm/MultiProvider, no direct Google Cloud
  usage.

Dev deps (``[dependency-groups] dev``):
- ``black>=25.1.0`` — never invoked; ruff format does it and is what
  pre-commit + Makefile actually call.
- ``isort>=6.0.1`` — never invoked; ruff's ``I`` lint set handles
  imports. (pylint pulls isort transitively, so functionality is
  preserved.)

ruff (27) and mypy (82) baselines unchanged; ``uv sync`` uninstalls
~15 packages.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -33,7 +33,6 @@ classifiers = [
   "Programming Language :: Python :: 3.14",
 ]
 dependencies = [
-  "litellm[proxy]>=1.83.0",
   "openai-agents[litellm]==0.14.6",
   "pydantic[email]>=2.11.3",
   "rich",
@@ -44,14 +43,12 @@ dependencies = [
   "traceloop-sdk>=0.53.0",
   "opentelemetry-exporter-otlp-proto-http>=1.40.0",
   "scrubadub>=2.0.1",
-  "defusedxml>=0.7.1",
 ]
 
 [project.scripts]
 strix = "strix.interface.main:main"
 
 [project.optional-dependencies]
-vertex = ["google-cloud-aiplatform>=1.38"]
 sandbox = [
   "fastapi",
   "uvicorn",
@@ -59,9 +56,7 @@ sandbox = [
   "openhands-aci>=0.3.0",
   "playwright>=1.48.0",
   "gql[requests]>=3.5.3",
-  "pyte>=0.8.1",
   "libtmux>=0.46.2",
-  "numpydoc>=1.8.0",
 ]
 
 [dependency-groups]
@@ -72,8 +67,6 @@ dev = [
   "pylint>=3.3.7",
   "bandit>=1.8.3",
   "pre-commit>=4.2.0",
-  "black>=25.1.0",
-  "isort>=6.0.1",
   "pyinstaller>=6.17.0; python_version >= '3.12' and python_version < '3.15'",
 ]