fix: allow integration tests to run via test:integration script

Remove vitest exclude for integration.test.ts — tests self-gate
via describe.runIf(process.env.OPENSHELL_TEST) so they're skipped
in normal `pnpm test` runs but can execute with `pnpm test:integration`.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rrodrigu3z

vitest.config.ts

@@ -4,7 +4,6 @@ export default defineConfig({
   test: {
     environment: "node",
     include: ["src/__tests__/**/*.test.ts"],
-    exclude: ["src/__tests__/integration.test.ts"],
     coverage: {
       provider: "v8",
       reporter: ["text", "json", "html"],