fix(model-fetch): support /models for Anthropic-compat subpath providers

Providers like DeepSeek, Kimi, Zhipu GLM and MiniMax expose the
Anthropic-compatible API on a subpath (e.g. /anthropic) while the
OpenAI-style /models endpoint lives at the API root. The previous
heuristic blindly appended /v1/models to the Base URL, so every such
provider returned 404 and the UI mislabeled it as "provider does not
support fetching models".

Backend now generates a candidate list and tries them in order:
preset override -> baseURL /v1/models -> stripped-subpath /v1/models ->
stripped-subpath /models. Non-404/405 responses (auth, network) stop
immediately so we never retry against hostile status codes. Known
compat suffixes are kept in a length-descending constant so the
longest match wins; response bodies are truncated to 512 chars to
avoid HTML 404 pages bloating the error string.

Preset type gains an optional modelsUrl (DeepSeek points at
https://api.deepseek.com/models). Frontend threads the override
through fetchModelsForConfig when the current Base URL still matches
the preset default. A new fetchModelsEndpointNotFound i18n key
replaces the misleading "not supported" toast for exhausted-candidate
and 404/405 cases (zh/en/ja).

src/config/claudeProviderPresets.ts

@@ -66,6 +66,10 @@ export interface ProviderPreset {
 
   // 是否在 UI 中隐藏该预设（预设仍存在，仅不在列表中显示）
   hidden?: boolean;
+
+  // 获取模型列表使用的完整 URL（覆写自动候选逻辑）
+  // 缺省时后端基于 baseURL 自动尝试 /v1/models、/models 以及剥离已知兼容子路径后的变体。
+  modelsUrl?: string;
 }
 
 export const providerPresets: ProviderPreset[] = [
@@ -136,6 +140,8 @@ export const providerPresets: ProviderPreset[] = [
       },
     },
     category: "cn_official",
+    // Anthropic 兼容层挂在 /anthropic 子路径；/models 是根上独立端点
+    modelsUrl: "https://api.deepseek.com/models",
     icon: "deepseek",
     iconColor: "#1E88E5",
   },