ci: raise the coverage gate to 90 percent; docs: reconcile OAuth docs with the implementation

pyproject.toml

@@ -127,7 +127,7 @@ disallow_untyped_defs = false
 
 [tool.pytest.ini_options]
 minversion = "8.0"
-addopts = "-ra -q --strict-markers --cov=aegis_gitea_mcp --cov-report=term-missing --cov-fail-under=80"
+addopts = "-ra -q --strict-markers --cov=aegis_gitea_mcp --cov-report=term-missing --cov-fail-under=90"
 testpaths = ["tests"]
 pythonpath = ["src"]
 asyncio_mode = "auto"
@@ -141,7 +141,7 @@ source = ["src"]
 omit = ["tests/*", "**/__pycache__/*"]
 
 [tool.coverage.report]
-fail_under = 80
+fail_under = 90
 exclude_lines = [
     "pragma: no cover",
     "def __repr__",