ci: split PR and release certification gates (#161)

vitest.pr.config.ts

@@ -0,0 +1,16 @@
+import { defineConfig } from 'vitest/config';
+
+// Pull requests use changed-line coverage as a review signal. Release tags use
+// vitest.config.ts, whose narrow 100% per-file contract remains unchanged.
+export default defineConfig({
+  test: {
+    include: ['src/**/*.test.ts'],
+    coverage: {
+      provider: 'v8',
+      include: ['src/**/*.ts'],
+      exclude: ['src/**/*.test.ts', 'src/**/__tests__/**', 'src/types/**'],
+      reporter: ['json'],
+      reportsDirectory: 'coverage-pr',
+    },
+  },
+});