Add shared room scoring backend

[halfdimension]

Adds in-memory shared room scoring for multiplayer room catches.

• Adds room score model and room score service
• Adds scoreboard endpoint for room members
• Scoreboard includes all current room members, including zero-score players
• Successful shared creature catch increments catcher score and catch count
• Duplicate catch cannot double-increment score
• Scoreboard is sorted by score, catches, last catch time, and display name
• Adds backend tests for scoreboard access, score updates, duplicate protection, and sorting
• Keeps frontend, DB persistence, Redis, global leaderboard, WebSocket behavior, and solo gameplay out of scope