Refactor/backend cleanup

[tasaje1]

Description

This PR refactors the backend package layout to a clearer feature-oriented structure with explicit layer boundaries (api, application, domain, infrastructure/shared).

Goal: improve maintainability, reduce package ambiguity, and make ownership/responsibilities easier to understand.

What Was Refactored

• Split websocket responsibilities into feature APIs vs shared websocket infrastructure.
• Consolidated lobby into:
  • lobby.api
  • lobby.application
  • lobby.domain
• Consolidated game into:
  • game.api
  • game.application
  • game.domain
  • game.mapping
  • game.api.dto
• Consolidated chat into:
  • chat.api
  • chat.application
  • chat.domain
  • chat.api.dto
• Consolidated recovery into:
  • recovery.application
  • recovery.domain.snapshot
  • recovery.infrastructure
• Moved shared technical config to:
  • shared.config
• Moved websocket infrastructure to:
  • shared.websocket
• Removed the legacy utility bucket by moving enums into feature-owned packages.

Key Class Renames

• GameController -> LobbySocketController
• CardDataTransferObject -> CardDto
• GameStateDataTransferObject -> GameStateDto

Notes

• Structural refactor only (no intended behavior change).
• Imports/tests were updated to match the new package and type names.

Package Structure (High-Level)

backend
├─ shared
│  ├─ config
│  └─ websocket
├─ lobby
│  ├─ api
│  │  └─ dto
│  ├─ application
│  └─ domain
├─ game
│  ├─ api
│  │  └─ dto
│  ├─ application
│  ├─ domain
│  └─ mapping
├─ chat
│  ├─ api
│  │  └─ dto
│  ├─ application
│  └─ domain
└─ recovery
   ├─ application
   ├─ domain
   │  └─ snapshot
   └─ infrastructure

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
97.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[XtophB]

LGTM, final warnings are fixed.
We have warnings about local field variables in some tests. Can be fixed in the future, we might need the variables in the future

[the-only-queen-anna]

Grundsätzlich LGTM; sehr saubere Struktur mMn.
LobbySocketController wird aber soweit ich weiß nie verwendet, eventuell überdenken, ob / wofür wir den noch brauchen (Stichwort reconnect?)