Discover Pi Webster models dynamically

[theFong]

Summary

• discover every Webster model available to the supplied key from /v1/models
• generate Pi model entries with per-model context and output limits
• preserve an accessible existing default, prefer glm-5.2 when available, and validate explicit PI_MODEL choices
• detect model-access drift in --check while preserving installed models during offline re-runs
• fail cleanly for rejected keys and keys with no accessible models

Validation

• bash -n install.sh
• bash -n pi-setup.sh
• ./test.sh
• git diff --check
• actionlint .github/workflows/bootstrap.yml
• live Webster discovery and local Pi reinstall
• pi-setup.sh --check
• pi --list-models webster shows all four models available to the current key