feat(health-check): replace real-LLM probe with HTTP reachability check

The provider panel health check sent a real streaming model request, which many third-party providers block (401/403/WAF), causing false negatives while only stable official endpoints passed. Replace it with a lightweight reachability probe: GET the provider base_url and treat any HTTP response (200/4xx/5xx) as reachable; only DNS/connect/TLS/timeout count as failure. Latency is the probe's TTFB.

Backend (services/stream_check.rs): rewrite ~2200 -> ~350 lines, dropping real-request building, format conversion, auth and API-path resolution while keeping per-app base_url extraction. Defaults: 8s timeout, 1 retry, 1500ms degraded threshold.

Failover invariant: the reachability check must never reset the circuit breaker (reachable != usable; a 403 host is reachable but broken for real traffic). Remove the resetCircuitBreaker call from useStreamCheck; failover failure detection stays driven solely by real proxy traffic (forwarder/circuit_breaker untouched). useResetCircuitBreaker is kept dormant for a future manual-recovery entry.

Open the check to all providers: drop the official/copilot/codex-oauth/third-party gating and the 'sends a real request' confirm dialog. For official providers whose base_url is intentionally empty, fall back to the endpoint the client actually uses (Claude -> api.anthropic.com, Codex -> chatgpt.com/backend-api/codex, Gemini -> generativelanguage). Non-official providers with a missing base_url still error to avoid a false green light. Claude Desktop Official is native 1P mode (talks to claude.ai, cc-switch not in the request path, no reliable endpoint) so its button stays hidden.

Slim StreamCheckConfig and per-provider testConfig to timeout/threshold/retries (drop test model + prompt); sync zh/en/ja/zh-TW. Retain the now-unused anthropic_to_openai/anthropic_to_gemini transform utilities and their test suites.

src-tauri/src/proxy/providers/mod.rs

@@ -48,8 +48,7 @@ pub use claude::{
 pub use codex::CodexAdapter;
 pub use codex::{
     apply_codex_chat_upstream_model, codex_provider_upstream_model,
-    codex_provider_uses_chat_completions, is_origin_only_url, resolve_codex_chat_reasoning_config,
-    should_convert_codex_responses_to_chat,
+    resolve_codex_chat_reasoning_config, should_convert_codex_responses_to_chat,
 };
 pub use gemini::GeminiAdapter;
 

src-tauri/src/proxy/providers/transform.rs

@@ -112,6 +112,10 @@ pub fn resolve_reasoning_effort(body: &Value) -> Option<&'static str> {
 }
 
 /// Anthropic 请求 → OpenAI Chat Completions 请求
+///
+/// 转换工具库 API：当前无生产调用方（连通性检查不再发真实请求，曾是其唯一 crate 内
+/// 消费者），但保留其转换逻辑与下方测试套件，供代理转换路径复用 / 未来接线。
+#[allow(dead_code)]
 pub fn anthropic_to_openai(body: Value) -> Result<Value, ProxyError> {
     anthropic_to_openai_with_reasoning_content(body, false)
 }

src-tauri/src/proxy/providers/transform_gemini.rs

@@ -39,6 +39,11 @@ pub(crate) fn is_synthesized_tool_call_id(id: &str) -> bool {
     id.starts_with(SYNTHESIZED_ID_PREFIX)
 }
 
+/// Anthropic 请求 → Gemini 原生请求。
+///
+/// 转换工具库 API：当前无生产调用方（连通性检查不再发真实请求，曾是其唯一 crate 内
+/// 消费者），但保留其转换逻辑与下方测试套件，供代理转换路径复用 / 未来接线。
+#[allow(dead_code)]
 pub fn anthropic_to_gemini(body: Value) -> Result<Value, ProxyError> {
     anthropic_to_gemini_with_shadow(body, None, None, None)
 }