fix: use standard dist/ output for Vite, copy to static/ explicitly

The relative outDir '../src/main/resources/static' resolved
unpredictably in Docker. Use standard 'dist/' output, then:
- Dockerfile: COPY --from=frontend /ui/dist/ to static/
- CI: cp -r dist/ to src/main/resources/static/

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

ui/vite.config.ts

@@ -13,7 +13,7 @@ export default defineConfig({
     },
   },
   build: {
-    outDir: '../src/main/resources/static',
+    outDir: 'dist',
     emptyOutDir: true,
   },
 });