Discover OpenCode models for canonical runtime profiles

[dcellison]

Closes #727.

Summary

• add principal-scoped OpenCode model discovery through the documented headless server /provider API
• run discovery under each runtime profile's effective OS-user, configuration, provider, and authentication context
• preserve nested provider/model identifiers while retaining only bounded, non-secret model metadata
• bind the short-lived metadata server to loopback, protect it with a random per-run password, and reap it on success, failure, timeout, or cancellation
• register OpenCode with the canonical model catalogue without changing OpenCode's safe free-text model entry or any current/default selection
• normalize Claude, Codex, and OpenCode discovery provenance IDs so successful observations pass the canonical catalogue validator

Safety and fallback

• no model, session, prompt, or generation endpoint is invoked
• control-plane credentials and inherited one-turn OpenCode model overrides are stripped
• provider options, request headers, API keys, costs, and raw response bodies are never persisted
• disconnected providers are classified as authentication failures; unknown providers remain unsupported, leaving the explicit configured model available
• catalogue timeouts and refresh failures retain the existing last-known-good inventory and selected model

Validation

• make check
• focused cross-adapter catalogue, lifecycle, and application-host tests: 36 passed
• full suite: 6200 passed

Protocol references

• OpenCode server API: https://opencode.ai/docs/server/
• OpenCode generated provider types: https://github.com/anomalyco/opencode/blob/v1.15.11/packages/sdk/js/src/gen/types.gen.ts