feat(hub): derive admin model picker from org provider connection via OpenRouter API

The admin role model picker was hardcoded to the env-default model registry
(createDefaultModelRegistry), which only ever returned a single Sonnet model.
Roles could not select any other model regardless of what the org's provider
connection supported.

Replace the env-only model list with a ProviderModelCatalog that:
- Resolves the org's ACTIVE provider connection credential (BYOK or
  platform-managed, encrypted via ADR-0024 envelope)
- Calls OpenRouter GET /v1/models?supported_parameters=tools to list
  tool-capable models available to that org
- Caches results in-memory with a 5-minute TTL per organization
- Falls back to the env-default registry when no ACTIVE provider exists

The runtime modelRegistry no longer validates role.defaultModel against the
env model list — the admin already validated by selection from the provider
catalog. The env list remains as the fallback for roles with null defaultModel.

The admin roles page loads models independently (non-blocking) so roles
remain editable even if the provider API is slow or unreachable.

hub/src/admin/routes/orgRoutes.ts

@@ -116,6 +116,7 @@ export async function registerOrgRoutes(app: FastifyInstance, config: OrgRouteCo
     prisma: config.prisma,
     sessionSecret: config.sessionSecret,
     skillStoreRoot: readSkillStoreRoot(),
+    secretEnvelope: config.secretEnvelope,
   });
   await registerSessionsAndUsageRoutes(app, {
     prisma: config.prisma,