Restore nest coverage to >=80% after the #1209 dep bump (istanbul provider + branch tests) (#1213)

* fix(server): set oxc:false in vitest so the SWC transform survives the Vite 8 bump

* fix(server): switch coverage to the istanbul provider (v8 under-reports branches on Vite 8 + Vitest 4)

* test(nest): cover controller/service branches to clear the 80% coverage gate

server/vitest.config.ts

@@ -24,7 +24,11 @@ export default defineConfig({
     silent: false,
     reporters: ['verbose'],
     coverage: {
-      provider: 'v8',
+      // Vite 8 + Vitest 4 made the sourcemap-based `v8` provider under-report branch
+      // coverage on the SWC/decorator-transformed output (it dropped to ~68% even
+      // though every test passes). `istanbul` instruments the source directly, so
+      // coverage is measured independently of the transform pipeline.
+      provider: 'istanbul',
       reporter: ['lcov', 'text'],
       reportsDirectory: './coverage',
       include: ['src/**/*.ts'],