feat(pi): fetch and refresh upstream model lists, searchable model picker

- POST /pi/upstreams/{id}/models/refresh calls the provider's model list
  endpoint (OpenAI-shaped /models, Anthropic /v1/models, Google
  /v1beta/models, OpenRouter /api/v1/models; Radius via pi-ai refresh),
  normalizes {id, displayName, contextWindow, supportsVision,
  supportsTools, pricing} and stores it in pi_upstream.models (0044)
- GET .../models returns {source, fetchedAt, models[]}: remote merged
  with the static catalog (remote first); failures (401/network/
  unsupported) fall back to static with a one-line error
- POST /pi/models/probe for trying credentials before creating
- wizard and edit drawer: fetch button, searchable dropdown with
  vision/tool tags, manual id, source line; default upstream needs a model
- tests: mock /models, 401, network failure; smoke step; runbook

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/db/src/types.ts

@@ -1086,6 +1086,8 @@ export interface PiUpstreamTable {
   oauth_expires_at: Timestamptz | null;
   created_at: GeneratedTimestamptz;
   updated_at: GeneratedTimestamptz;
+  models: Json | null;
+  models_fetched_at: Timestamptz | null;
 }
 
 export interface PolicyRevisionTable {