Make test results copyable

Add Markdown formatting utilities for test results, wire up clipboard copy in IntegrationTestRunner, and export new formatters. Introduce formatters.ts, extend index.ts exports, and implement copy all / copy failed / per-test copy functionality with updated UI.

src/lib/integrationTests/index.ts

@@ -6,5 +6,6 @@
 
 export { IntegrationTestRunner } from './testRunner';
 export { allTestSuites } from './suites';
+export { formatResultsAsMarkdown, formatSingleTestAsMarkdown } from './formatters';
 
 export type { TestResult, Test, TestSuite } from './testRunner';