feat(usage): add auto-refresh interval for usage queries

New Features:
- Users can configure auto-query interval in "Configure Usage Query" dialog
- Interval in minutes (0 = disabled, recommend 5-60 minutes)
- Auto-query only enabled for currently active provider
- Display last query timestamp in relative time format (e.g., "5 min ago")
- Execute first query immediately when enabled, then repeat at intervals

Technical Implementation:
- Backend: Add auto_query_interval field to UsageScript struct
- Frontend: Create useAutoUsageQuery Hook to manage timers and query state
- UI: Add auto-query interval input field in UsageScriptModal
- Integration: Display auto-query results and timestamp in UsageFooter
- i18n: Add Chinese and English translations

UX Improvements:
- Minimum interval protection (1 minute) to prevent API abuse
- Auto-cleanup timers on component unmount
- Silent failure handling for auto-queries, non-intrusive to users
- Prioritize auto-query results, fallback to manual query results
- Timestamp display positioned next to refresh button for better clarity

src/i18n/locales/en.json

@@ -338,7 +338,11 @@
     "invalid": "Expired",
     "total": "Total:",
     "used": "Used:",
-    "remaining": "Remaining:"
+    "remaining": "Remaining:",
+    "justNow": "Just now",
+    "minutesAgo": "{{count}} min ago",
+    "hoursAgo": "{{count}} hr ago",
+    "daysAgo": "{{count}} day ago"
   },
   "usageScript": {
     "title": "Configure Usage Query",
@@ -355,6 +359,8 @@
     "queryFailedMessage": "Query failed",
     "queryScript": "Query script (JavaScript)",
     "timeoutSeconds": "Timeout (seconds)",
+    "autoQueryInterval": "Auto Query Interval (minutes)",
+    "autoQueryIntervalHint": "0 to disable, recommend 5-60 minutes",
     "scriptHelp": "Script writing instructions:",
     "configFormat": "Configuration format:",
     "commentOptional": "optional",