v0.13.0

v0.13.0 — track aicodebox v0.13.0, client-executed tool calling + schema

OpenAI-style client-executed tool calling on /openai/v1/chat/completions,
composable with response_format so an agentic multi-tool flow can end in
a schema-validated structured JSON reply. A tool-call turn -> tool_calls
/ finish_reason=tool_calls (not schema-checked); the final-answer turn ->
schema-validated JSON / finish_reason=stop (exhausted retries -> 422,
crash -> 500). tools + stream:true -> 400. The OAI endpoint now defaults
tools-off; opt in with x-aicodebox-no-tools: false or a tools-allowlist.

PiAdapter unchanged — tool calling + schema composition are base-side.
Base pinned to psyb0t/aicodebox:v0.13.0. Two new real end-to-end
tool-calling tests against a live GLM model. Minor bump.

49/49 tests green. Built against psyb0t/aicodebox:v0.13.0.