feat: add Docker deployment support and fix /users/me endpoint

- Add docker/ directory with Dockerfile for backend and frontend
- Backend: pytorch/pytorch CUDA base image with all qwen_tts deps
- Frontend: multi-stage nginx build with /api/ proxy to backend
- docker-compose.yml (CPU) + docker-compose.gpu.yml (GPU overlay)
- Fix /users/me returning 404 due to missing route (was caught by /{user_id})
- Update .gitignore to exclude docker/models, docker/data, docker/.env
- Update README and README.zh.md with Docker deployment instructions

Images: bdim404/qwen3-tts-backend, bdim404/qwen3-tts-frontend

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

docker/docker-compose.gpu.yml

@@ -0,0 +1,9 @@
+services:
+  backend:
+    deploy:
+      resources:
+        reservations:
+          devices:
+            - driver: nvidia
+              count: 1
+              capabilities: [gpu]