feat: add max_claude_code_version setting and disable auto-upgrade env var

Add maximum Claude Code version limit to complement the existing minimum
version check. Refactor the version cache from single-value to unified
bounds struct (min+max) with a single atomic.Value and singleflight group.

- Backend: new constant, struct field, cache refactor, validation (semver
  format + cross-validation max >= min), gateway enforcement, audit diff
- Frontend: settings UI input, TypeScript types, zh/en i18n
- Add CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 to all Claude Code
  tutorials on /keys page (unix/cmd/powershell/vscode settings.json)

frontend/src/api/admin/settings.ts

@@ -81,6 +81,7 @@ export interface SystemSettings {
 
   // Claude Code version check
   min_claude_code_version: string
+  max_claude_code_version: string
 
   // 分组隔离
   allow_ungrouped_key_scheduling: boolean
@@ -137,6 +138,7 @@ export interface UpdateSettingsRequest {
   ops_query_mode_default?: 'auto' | 'raw' | 'preagg' | string
   ops_metrics_interval_seconds?: number
   min_claude_code_version?: string
+  max_claude_code_version?: string
   allow_ungrouped_key_scheduling?: boolean
 }