M39: harden application and acceptance gates

backend/pyproject.toml

@@ -15,7 +15,6 @@ dependencies = [
   "psycopg[binary]>=3.2,<4",
   "alembic>=1.13,<2",
   "httpx>=0.27,<1",
-  "httpx2>=2.10,<3",
   "authlib>=1.6,<2",
   "itsdangerous>=2.2,<3",
   "prometheus-client>=0.24,<1"
@@ -24,7 +23,8 @@ dependencies = [
 [project.optional-dependencies]
 dev = [
   "pytest>=8,<9",
-  "pytest-asyncio>=0.24,<1",
+  # Starlette's TestClient (>=1.0) prefers httpx2 and warns when only httpx is present.
+  "httpx2>=2.10,<3",
   "ruff>=0.8,<1",
   "mypy>=1.13,<2"
 ]
@@ -34,7 +34,6 @@ packages = ["app"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
-asyncio_mode = "auto"
 
 [tool.ruff]
 line-length = 100