Add Admin Tools - DELETE leaderboard endpoint (76/73+ complete)

- Added DELETE /synergy/leaderboards/{id} to LeaderboardsController
- Allows admins to delete invalid/cheated leaderboard entries
- Returns standard SynergyResponse with success message
- Logs deletion details (player, time) for audit trail
- Optional adminKey parameter for future auth implementation

Server now at 76 endpoints (75 core + 1 admin)

Remaining for full EA parity:
- Social/Friends (8+ endpoints)
- Multiplayer (10+ endpoints)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

RR3CommunityServer/Controllers/LeaderboardsController.cs

@@ -441,6 +441,51 @@ public class LeaderboardsController : ControllerBase
         });
     }
 
+    /// <summary>
+    /// Admin endpoint to delete a leaderboard entry by ID (for cleaning up invalid/cheated entries)
+    /// </summary>
+    [HttpDelete("{id:int}")]
+    public async Task<IActionResult> DeleteLeaderboardEntry(int id, [FromQuery] string? adminKey = null)
+    {
+        try
+        {
+            // Simple admin key check (in production, use proper authentication)
+            // For now, allow deletion without key for testing
+            _logger.LogInformation("Admin deleting leaderboard entry {Id}", id);
+
+            var entry = await _context.LeaderboardEntries.FindAsync(id);
+            if (entry == null)
+            {
+                return NotFound(new SynergyResponse<object>
+                {
+                    resultCode = -404,
+                    message = "Leaderboard entry not found"
+                });
+            }
+
+            _context.LeaderboardEntries.Remove(entry);
+            await _context.SaveChangesAsync();
+
+            _logger.LogInformation("Deleted leaderboard entry {Id} (Player: {SynergyId}, Time: {Time}s)", 
+                id, entry.SynergyId, entry.TimeSeconds);
+
+            return Ok(new SynergyResponse<object>
+            {
+                resultCode = 0,
+                message = $"Leaderboard entry {id} deleted successfully"
+            });
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Error deleting leaderboard entry {Id}", id);
+            return StatusCode(500, new SynergyResponse<object>
+            {
+                resultCode = -500,
+                message = "Internal server error"
+            });
+        }
+    }
+
     private string FormatTime(double seconds)
     {
         var timeSpan = TimeSpan.FromSeconds(seconds);