test: add @vitest/coverage-v8 + test:coverage to all workspaces

apps/api/vitest.config.ts

@@ -5,5 +5,13 @@ export default defineConfig({
     environment: 'node',
     setupFiles: ['./test/setup.ts'],
     fileParallelism: false,
+    coverage: {
+      provider: 'v8',
+      all: true,
+      reporter: ['text', 'json-summary'],
+      include: ['src/**'],
+      // Generated / non-logic files: excluded with intent (not silent gaps).
+      exclude: ['src/db/schema.ts', 'src/index.ts', '**/*.d.ts'],
+    },
   },
 });