fix(keys): grok-4.5 上下文窗口按 500k 对齐并修正账号测试 i18n mock

- UseKeyModal 中 grok-4.5 的 context_window / model_context_window /
  OpenCode 模型目录统一改为 500000，与 xAI 实际上下文一致
- UseKeyModal.spec 的 OpenCode 目录断言同步为 500000
- AccountTestModal.spec 补齐 imagePreviewAlt 的 i18n mock，
  跟上组件把 alt 文案迁到 i18n 之后的行为

frontend/src/components/admin/account/__tests__/AccountTestModal.spec.ts

@@ -33,6 +33,9 @@ vi.mock('vue-i18n', async () => {
         if (key === 'admin.accounts.imageReceived' && params?.count) {
           return `received-${params.count}`
         }
+        if (key === 'admin.accounts.imagePreviewAlt' && params?.index) {
+          return `test-image-${params.index}`
+        }
         return messages[key] || key
       }
     })

frontend/src/components/keys/UseKeyModal.vue

@@ -826,7 +826,7 @@ description = "Grok 4.5 via Sub2API (Responses)"
 # base_url = "${baseUrl}"
 env_key = "XAI_API_KEY"                     # or: api_key = "${apiKey}"  (not recommended)
 api_backend = "responses"                   # chat_completions | responses | messages
-context_window = 1000000                    # drives auto-compaction timing
+context_window = 500000                     # drives auto-compaction timing
 # Optional sampling (global defaults can live under [models] instead):
 # temperature = 0.7
 # top_p = 0.95
@@ -941,7 +941,7 @@ model = "grok-4.5"
 # Optional:
 # review_model = "grok-4.5"
 # model_reasoning_effort = "medium"
-# model_context_window = 1000000
+# model_context_window = 500000
 # disable_response_storage = true
 # network_access = "enabled"
 # windows_wsl_setup_acknowledged = true
@@ -1482,7 +1482,7 @@ function generateOpenCodeConfig(platform: string, baseUrl: string, apiKey: strin
   const grokModels = {
     'grok-4.5': {
       name: 'Grok 4.5',
-      limit: { context: 1000000, output: 64000 }
+      limit: { context: 500000, output: 64000 }
     },
     'grok-build-0.1': {
       name: 'Grok Build 0.1',

frontend/src/components/keys/__tests__/UseKeyModal.spec.ts

@@ -106,7 +106,7 @@ describe('UseKeyModal', () => {
       apiKey: 'sk-grok-test'
     })
     expect(parsed.provider.grok.models['grok-4.5']).toBeDefined()
-    expect(parsed.provider.grok.models['grok-4.5'].limit.context).toBe(1000000)
+    expect(parsed.provider.grok.models['grok-4.5'].limit.context).toBe(500000)
     expect(parsed.provider.grok.models['grok-build-0.1']).toBeDefined()
     expect(parsed.provider.grok.models['grok-4.20-multi-agent-0309']).toBeDefined()
     expect(parsed.provider.grok.models['grok-composer-2.5-fast']).toBeDefined()