fix(i18n,api): backfill missing token-monitoring keys and fix JWT expiry tz

- i18n: add models.searchProviders, monitoring.tabs.tokens and the
  monitoring.tokens.* block (incl. bucket.hour/day) to es-ES, ja-JP,
  ru-RU, th-TH, vi-VN and zh-Hant, which were missing them and failed
  the Check i18n Keys CI.
- api: generate_jwt_token built 'exp' from a naive datetime.now(), which
  PyJWT validates against UTC — in any timezone ahead of UTC the token
  was already expired at issue time. Use datetime.now(timezone.utc).

web/src/i18n/locales/zh-Hant.ts

@@ -250,6 +250,7 @@ const zhHant = {
     selectProvider: '選擇供應商',
     requester: '供應商類型',
     selectRequester: '選擇供應商類型',
+    searchProviders: '搜尋供應商...',
     langbotModelsDescription: '由 LangBot Space 提供的雲端模型',
     credits: '積分',
     loginWithSpace: '使用 Space 登入',
@@ -1146,6 +1147,7 @@ const zhHant = {
       llmCalls: 'LLM調用',
       embeddingCalls: 'Embedding調用',
       modelCalls: '模型調用',
+      tokens: 'Token 監控',
       sessions: '會話分析',
       feedback: '使用者反饋',
       errors: '錯誤日誌',
@@ -1184,6 +1186,30 @@ const zhHant = {
       avgDuration: '平均持續時間',
       calls: '呼叫次數',
     },
+    tokens: {
+      totalTokens: '總 Token 數',
+      inputTokens: '輸入 Token',
+      outputTokens: '輸出 Token',
+      avgPerCall: '平均每次呼叫',
+      throughput: '吞吐量',
+      tokensPerSec: 'Token/秒',
+      errorCalls: '失敗呼叫',
+      acrossCalls: '共 {{count}} 次呼叫',
+      ofTotal: '共 {{count}} 次',
+      usageOverTime: 'Token 用量趨勢',
+      byModel: '按模型統計',
+      model: '模型',
+      calls: '呼叫次數',
+      avgLatency: '平均延遲',
+      noData: '所選時間範圍內暫無 Token 用量資料',
+      loadError: '載入 Token 統計失敗：{{error}}',
+      zeroTokenWarning:
+        '偵測到 {{count}} 次成功呼叫未上報 Token 用量（記為 0）。這通常表示上游未返回 usage 資訊，請檢查模型供應商設定。',
+      bucket: {
+        hour: '按小時',
+        day: '按天',
+      },
+    },
     embeddingCalls: {
       title: 'Embedding調用',
       model: '模型',