fix: improve cost tracking accuracy for modern models

- Added support for reasoning tokens in cost calculations.
- Fixed DeepSeek cache-write token mapping (PromptCacheMissTokens).
- Improved CalculateCost debug logging to trace all pricing variables.

internal/server/server.go

@@ -378,9 +378,9 @@ func (s *Server) logRequest(start time.Time, clientID, provider, model string, u
 		}
 		
 		// Calculate cost using registry
-		entry.Cost = utils.CalculateCost(s.registry, model, entry.PromptTokens, entry.CompletionTokens, entry.CacheReadTokens, entry.CacheWriteTokens)
-		fmt.Printf("[DEBUG] Request logged: model=%s, prompt=%d, completion=%d, cache_read=%d, cost=%f\n", 
-			model, entry.PromptTokens, entry.CompletionTokens, entry.CacheReadTokens, entry.Cost)
+		entry.Cost = utils.CalculateCost(s.registry, model, entry.PromptTokens, entry.CompletionTokens, entry.ReasoningTokens, entry.CacheReadTokens, entry.CacheWriteTokens)
+		fmt.Printf("[DEBUG] Request logged: model=%s, prompt=%d, completion=%d, reasoning=%d, cache_read=%d, cost=%f\n", 
+			model, entry.PromptTokens, entry.CompletionTokens, entry.ReasoningTokens, entry.CacheReadTokens, entry.Cost)
 	}
 
 	s.logger.LogRequest(entry)