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/components/keys/UseKeyModal.vue

@@ -441,17 +441,20 @@ function generateAnthropicFiles(baseUrl: string, apiKey: string): FileConfig[] {
     case 'unix':
       path = 'Terminal'
       content = `export ANTHROPIC_BASE_URL="${baseUrl}"
-export ANTHROPIC_AUTH_TOKEN="${apiKey}"`
+export ANTHROPIC_AUTH_TOKEN="${apiKey}"
+export CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1`
       break
     case 'cmd':
       path = 'Command Prompt'
       content = `set ANTHROPIC_BASE_URL=${baseUrl}
-set ANTHROPIC_AUTH_TOKEN=${apiKey}`
+set ANTHROPIC_AUTH_TOKEN=${apiKey}
+set CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1`
       break
     case 'powershell':
       path = 'PowerShell'
       content = `$env:ANTHROPIC_BASE_URL="${baseUrl}"
-$env:ANTHROPIC_AUTH_TOKEN="${apiKey}"`
+$env:ANTHROPIC_AUTH_TOKEN="${apiKey}"
+$env:CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1`
       break
     default:
       path = 'Terminal'
@@ -466,6 +469,7 @@ $env:ANTHROPIC_AUTH_TOKEN="${apiKey}"`
   "env": {
     "ANTHROPIC_BASE_URL": "${baseUrl}",
     "ANTHROPIC_AUTH_TOKEN": "${apiKey}",
+    "CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC": "1",
     "CLAUDE_CODE_ATTRIBUTION_HEADER": "0"
   }
 }`