test: add wire-level service contract tests

tests/contracts sends the raw requests the code sends to Ollama (native API
and OpenAI-compat tool calling), Anthropic (including the pinned Sonnet 5
temperature-rejection contract), Qdrant, SearXNG, library-desk, and Redis.
Unreachable services skip; wrong response shapes fail. Run via
make test-contracts; excluded from the unit suite.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pyproject.toml

@@ -47,6 +47,7 @@ markers = [
     "unit: Unit tests",
     "integration: Integration tests",
     "slow: Slow running tests",
+    "contract: Wire-level contract tests against live service boundaries",
 ]
 addopts = [
     "--verbose",