feat: Agnes上下文512K→1M + Ollama支持配置num_ctx

Agnes AI:
- adapter注释和API文档更新: 上下文512K→1M (官方已升级)

Ollama num_ctx 支持:
- MetonaGenerationParams 新增 contextLength 字段
- OllamaAdapter.toNativeRequest 发送 options.num_ctx
- AgentLoopEngine 从 config 读取并传递到请求参数
- database.service 新增 ollama.numCtx 默认配置(null=由模型决定)
- SettingsModal LLM设置: Ollama 选中时显示上下文长度输入框
- main.ts 启动时从 configService 读取 ollama.numCtx

数据流:
Settings → configService → main.ts → AgentLoopEngine.config
→ MetonaRequest.params → OllamaAdapter → options.num_ctx

src/components/settings/SettingsModal.tsx

@@ -101,6 +101,7 @@ function LLMSettings() {
   const [model, setModel] = useConfig('llm.model', '');
   const [apiKey, setApiKey] = useConfig('llm.apiKey', '');
   const [baseURL, setBaseURL] = useConfig('llm.baseURL', '');
+  const [numCtx, setNumCtx] = useConfig('ollama.numCtx', null as number | null);
   const [showKey, setShowKey] = useState(false);
 
   return (
@@ -118,6 +119,20 @@ function LLMSettings() {
       <TextField size="small" label="API Key" type={showKey ? 'text' : 'password'} value={apiKey} onChange={(e) => setApiKey(e.target.value)} placeholder="sk-...（本地模型可留空）"
         slotProps={{ input: { endAdornment: <IconButton size="small" onClick={() => setShowKey(!showKey)}>{showKey ? <EyeOff size={14} /> : <Eye size={14} />}</IconButton> } }}
       />
+      {provider === 'ollama' && (
+        <TextField
+          size="small"
+          label="上下文长度 (num_ctx)"
+          type="number"
+          value={numCtx ?? ''}
+          onChange={(e) => {
+            const v = e.target.value;
+            setNumCtx(v === '' ? null : Number(v));
+          }}
+          placeholder="默认由模型决定（如 2048、4096、128000）"
+          slotProps={{ htmlInput: { min: 512, step: 512 } }}
+        />
+      )}
     </Stack>
   );
 }