chore: remove usage tracking and logging functionality

- Deleted the `LoggerPlugin` along with associated usage tracking and in-memory statistics logic.
- Removed all related tests (`logger_plugin_test.go`, `usage_tab_test.go`) and external-facing handler (`usage.go`) for usage statistics export/import.
- Cleaned up TUI integration by deleting `usage_tab.go`.

internal/redisqueue/plugin.go

@@ -7,7 +7,6 @@ import (
 	"time"
 
 	internallogging "github.com/router-for-me/CLIProxyAPI/v6/internal/logging"
-	internalusage "github.com/router-for-me/CLIProxyAPI/v6/internal/usage"
 	coreusage "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/usage"
 )
 
@@ -21,7 +20,7 @@ func (p *usageQueuePlugin) HandleUsage(ctx context.Context, record coreusage.Rec
 	if p == nil {
 		return
 	}
-	if !Enabled() || !internalusage.StatisticsEnabled() {
+	if !Enabled() || !UsageStatisticsEnabled() {
 		return
 	}
 
@@ -45,7 +44,7 @@ func (p *usageQueuePlugin) HandleUsage(ctx context.Context, record coreusage.Rec
 	apiKey := strings.TrimSpace(record.APIKey)
 	requestID := strings.TrimSpace(internallogging.GetRequestID(ctx))
 
-	tokens := internalusage.TokenStats{
+	tokens := tokenStats{
 		InputTokens:     record.Detail.InputTokens,
 		OutputTokens:    record.Detail.OutputTokens,
 		ReasoningTokens: record.Detail.ReasoningTokens,
@@ -64,7 +63,7 @@ func (p *usageQueuePlugin) HandleUsage(ctx context.Context, record coreusage.Rec
 		failed = !resolveSuccess(ctx)
 	}
 
-	detail := internalusage.RequestDetail{
+	detail := requestDetail{
 		Timestamp: timestamp,
 		LatencyMs: record.Latency.Milliseconds(),
 		Source:    record.Source,
@@ -74,7 +73,7 @@ func (p *usageQueuePlugin) HandleUsage(ctx context.Context, record coreusage.Rec
 	}
 
 	payload, err := json.Marshal(queuedUsageDetail{
-		RequestDetail: detail,
+		requestDetail: detail,
 		Provider:      provider,
 		Model:         modelName,
 		Endpoint:      resolveEndpoint(ctx),
@@ -89,7 +88,7 @@ func (p *usageQueuePlugin) HandleUsage(ctx context.Context, record coreusage.Rec
 }
 
 type queuedUsageDetail struct {
-	internalusage.RequestDetail
+	requestDetail
 	Provider  string `json:"provider"`
 	Model     string `json:"model"`
 	Endpoint  string `json:"endpoint"`
@@ -98,6 +97,23 @@ type queuedUsageDetail struct {
 	RequestID string `json:"request_id"`
 }
 
+type requestDetail struct {
+	Timestamp time.Time  `json:"timestamp"`
+	LatencyMs int64      `json:"latency_ms"`
+	Source    string     `json:"source"`
+	AuthIndex string     `json:"auth_index"`
+	Tokens    tokenStats `json:"tokens"`
+	Failed    bool       `json:"failed"`
+}
+
+type tokenStats struct {
+	InputTokens     int64 `json:"input_tokens"`
+	OutputTokens    int64 `json:"output_tokens"`
+	ReasoningTokens int64 `json:"reasoning_tokens"`
+	CachedTokens    int64 `json:"cached_tokens"`
+	TotalTokens     int64 `json:"total_tokens"`
+}
+
 func resolveSuccess(ctx context.Context) bool {
 	status := internallogging.GetResponseStatus(ctx)
 	if status == 0 {