refactor(usage): consolidate query logic to eliminate DRY violations

Breaking Changes:
- Removed useAutoUsageQuery hook (119 lines)
- Unified all usage queries into single useUsageQuery hook

Technical Improvements:
- Eliminated duplicate state management (React Query + manual useState)
- Fixed single source of truth principle violation
- Replaced manual setInterval with React Query's built-in refetchInterval
- Reduced UsageFooter complexity by 28% (54 → 39 lines)

New Features:
- useUsageQuery now accepts autoQueryInterval option
- Automatic query interval control (0 = disabled, min 1 minute)
- Built-in lastQueriedAt timestamp from dataUpdatedAt
- Auto-query only enabled for currently active provider

Architecture Benefits:
- Single data source: manual and auto queries share same cache
- No more state inconsistency between manual/auto query results
- Leverages React Query's caching, deduplication, and background updates
- Cleaner separation of concerns

Code Changes:
- src/lib/query/queries.ts: Enhanced useUsageQuery with auto-query support
- src/components/UsageFooter.tsx: Simplified to use single query hook
- src/hooks/useAutoUsageQuery.ts: Deleted (redundant)
- All type checks passed

src-tauri/src/lib.rs

@@ -539,8 +539,8 @@ pub fn run() {
             commands::delete_claude_mcp_server,
             commands::validate_mcp_command,
             // usage query
-            commands::query_provider_usage,
-            commands::test_usage_script,
+            commands::queryProviderUsage,
+            commands::testUsageScript,
             // New MCP via config.json (SSOT)
             commands::get_mcp_config,
             commands::upsert_mcp_server_in_config,