Move the AritmoLab provider (Qwen) into harness/.pi/extensions/ so it is
auto-discovered only when Pi runs with cwd=harness, keeping it project-local.
GLM (~/.pi/agent/models.json) and DeepSeek (built-in) stay user-wide. File is
.js (not .mjs) because Pi extension auto-discovery matches only /\.(ts|js)$/.
Removes the gemma4-26b-a4b model (404 at the endpoint) from both the provider
and the model-matrix default list.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
