Add tests, free-text model field, and K8s job improvements

- Add vitest with 26 passing tests for parse and job-manifest
- Set models to undefined for free-text model input
- Add fsGroupChangePolicy: "OnRootMismatch" to reduce volume chown delays
- Change job name prefix to agent-opencode- for adapter identification
- Add .npmrc to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vitest.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    include: ["src/**/*.test.ts"],
+    coverage: {
+      reporter: ["text", "json", "html"],
+    },
+  },
+});