Migrate test doubles + testSupport to ModelRuntime/InMemoryCredentialStore (slice 5)

Replace AuthStorage.inMemory / ModelRegistry.create|inMemory across all test
and support code with the pi-ai InMemoryCredentialStore + async
ModelRuntime.create({ credentials }). Add shared test-runtime seams
(createTestModelRuntime, testModelRuntime, seedCredential) in testSupport.ts
and thread modelRuntime into fakeRuntime and every PiSessionService
construction (now a required dependency). Rework the anthropic subscription
warning tests onto a temp auth.json seam read via readStoredCredential, and
the auth-loss warning test onto a live credential store + runtime refresh.
Make getLoginProviderOptions synchronous and fix associated await/lint sites.

npm run verify green (typecheck + lint + knip + 1390 tests).

src/server/sessions/authRoutes.ts

@@ -4,7 +4,7 @@ import type { AuthService } from "./authService.js";
 export function registerAuthRoutes(app: FastifyInstance, auth: AuthService, prefix = ""): void {
   app.get<{ Querystring: { mode?: "login" | "logout"; authType?: "oauth" | "api_key" } }>(`${prefix}/auth/providers`, async (request, reply) => {
     try {
-      return auth.authProviders(request.query.mode ?? "login", request.query.authType);
+      return await auth.authProviders(request.query.mode ?? "login", request.query.authType);
     } catch (error) {
       return reply.code(404).send({ error: error instanceof Error ? error.message : String(error) });
     }
@@ -12,7 +12,7 @@ export function registerAuthRoutes(app: FastifyInstance, auth: AuthService, pref
 
   app.post<{ Body: { providerId: string; key: string } }>(`${prefix}/auth/api-key`, async (request, reply) => {
     try {
-      return auth.saveApiKey(request.body.providerId, request.body.key);
+      return await auth.saveApiKey(request.body.providerId, request.body.key);
     } catch (error) {
       return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
     }
@@ -20,7 +20,7 @@ export function registerAuthRoutes(app: FastifyInstance, auth: AuthService, pref
 
   app.post<{ Body: { providerId: string } }>(`${prefix}/auth/logout`, async (request, reply) => {
     try {
-      return auth.logoutProvider(request.body.providerId);
+      return await auth.logoutProvider(request.body.providerId);
     } catch (error) {
       return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
     }
@@ -28,7 +28,7 @@ export function registerAuthRoutes(app: FastifyInstance, auth: AuthService, pref
 
   app.post<{ Body: { providerId: string } }>(`${prefix}/auth/oauth`, async (request, reply) => {
     try {
-      return auth.startOAuthLogin(request.body.providerId);
+      return await auth.startOAuthLogin(request.body.providerId);
     } catch (error) {
       return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
     }