[BUG]: WebSocket URLs hardcoded to ws://localhost:1313 — breaks any non-local deployment

### Bug Description

Several frontend WebSocket call sites hardcode the backend address instead of deriving it from `VITE_BASE_URL`:
- `frontend/src/components/Matchmaking.tsx` line 62
- (same pattern in other raw `new WebSocket(...)` call sites: `ChatRoom.tsx`, `TeamDebateRoom.tsx`, `Game.tsx`, `gamificationService.ts`)

`frontend/src/components/DebatePopup.tsx` line 31 also hardcodes `http://localhost:1313` for room creation.

## Impact
Matchmaking, chat, and room creation silently fail on any deployed environment (or even when the backend runs on a different port). The UI shows a permanent "connecting"/"Searching…" state with no error.

## Suggested Fix
Build WS URLs from `import.meta.env.VITE_BASE_URL` (swapping `http` → `ws`), in one shared helper.

### Steps to Reproduce

_No response_

### Logs and Screenshots

_No response_

### Environment Details

_No response_

### Impact

Critical - Application is unusable

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates

Start with the raw new WebSocket(...) call sites in frontend/src/components/Matchmaking.tsx, ChatRoom.tsx, TeamDebateRoom.tsx, Game.tsx, and gamificationService.ts, then inspect frontend/src/components/DebatePopup.tsx and the VITE_BASE_URL usage. Confirm the shared URL approach works for deployed and non-default backend addresses, and verify that matchmaking, chat, and room creation no longer use hardcoded localhost URLs.

Rédigé par le modèle d'indexation à partir du texte de l'issue.