ENHANCEMENTS: - RestAPI: add attendance PlayerCards mode

[Penfold-88]

Description

Adds an optimized PlayerCards mode to the /server_attendance REST API endpoint.

Global attendance

GET /server_attendance?PlayerCards=true

Server-specific attendance

GET /server_attendance?server_name=SERVER_NAME&PlayerCards=true

The response contains only the values required by the dashboard’s attendance cards:

{
  "current_players": 0,
  "unique_players_24h": 4,
  "unique_players_7d": 28,
  "unique_players_30d": 62
}

Performance

PlayerCards mode uses one count-only database query. It avoids calculating unnecessary:

• Playtime statistics
• Discord engagement
• Daily trends
• Top theatres
• Top missions
• Top modules
• Combat statistics

Backward Compatibility

• Omitting PlayerCards preserves the existing comprehensive response.
• PlayerCards=false preserves the existing comprehensive response.
• Global and server-specific filtering continue to work.
• Instance aliases and full DCS server names continue using the existing resolution logic.
• Existing integrations require no changes.

Testing

Tested against a running DCSServerBot instance:

• Global PlayerCards=true: HTTP 200 with exactly four fields.
• Server-specific PlayerCards=true: HTTP 200 with correctly filtered data.
• PlayerCards=false: HTTP 200 with the original 19-field response.
• Parameter omitted: HTTP 200 with the original 19-field response.