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-tauri/src/commands/model_fetch.rs

@@ -6,13 +6,20 @@ use crate::services::model_fetch::{self, FetchedModel};
 
 /// 获取供应商的可用模型列表
 ///
-/// 使用 OpenAI 兼容的 GET /v1/models 端点。
-/// 主要面向第三方聚合站（硅基流动、OpenRouter 等）。
+/// 使用 OpenAI 兼容的 GET /v1/models 端点。优先使用 `models_url` 精确覆写；
+/// 否则对 baseURL 生成候选列表（含「剥离 Anthropic 兼容子路径」兜底），按序尝试。
 #[tauri::command(rename_all = "camelCase")]
 pub async fn fetch_models_for_config(
     base_url: String,
     api_key: String,
     is_full_url: Option<bool>,
+    models_url: Option<String>,
 ) -> Result<Vec<FetchedModel>, String> {
-    model_fetch::fetch_models(&base_url, &api_key, is_full_url.unwrap_or(false)).await
+    model_fetch::fetch_models(
+        &base_url,
+        &api_key,
+        is_full_url.unwrap_or(false),
+        models_url.as_deref(),
+    )
+    .await
 }