test: add comprehensive coverage for OAuth scopes, MCP, and core services

Adds new and expanded test suites across client and server to cover the
OAuth 2.1 scope system, MCP session manager, collab service, unified
memories helpers, OIDC service, budget slice, and OAuth authorize page.
Also extends SonarQube coverage exclusions to include bootstrapping files
(migrations, scheduler, main.tsx, types.ts) that are not meaningfully
testable.

client/src/pages/DashboardPage.test.tsx

@@ -18,6 +18,12 @@ beforeEach(() => {
   seedStore(usePermissionsStore, {
     level: 'owner',
   } as any);
+  // Intercept CurrencyWidget's external fetch so it resolves before teardown
+  server.use(
+    http.get('https://api.exchangerate-api.com/v4/latest/:currency', () => {
+      return HttpResponse.json({ rates: { USD: 1.08, EUR: 1, CHF: 0.97 } });
+    }),
+  );
 });
 
 describe('DashboardPage', () => {