llm: 统一源接入层修复（对照 llmsproxy）

- provider: 新增 OpenAI-compatible 响应/流兜底解析，Lua adapter 异常时也能解析
  choices/message/tool_calls/usage（含 function.arguments 缺失、对象/字符串参数）
- 过滤无效 LLM 源（<nil>/空/缺 http(s) scheme），main 与 ReloadFromConfig 均跳过，
  避免 mocktest 等坏源污染 fallback 与 healthcheck
- adapter(openai/deepseek/groq/mistral/github/kimicode): 修 tool_calls 对
  nil function 的崩溃，兼容扁平/嵌套结构；openai 流透传 reasoning/tool_calls
- config: ToConfig 探活端点过滤无效 base_url，修复 supervisor 误报 LLM unreachable

internal/config/registry.go

@@ -695,6 +695,14 @@ func (r *ConfigRegistry) GetBool(key string, defaultVal bool) bool {
 	return b
 }
 
+func validLLMEndpoint(s string) bool {
+	s = strings.TrimSpace(s)
+	if s == "" || strings.EqualFold(s, "<nil>") || strings.EqualFold(s, "nil") || strings.EqualFold(s, "null") {
+		return false
+	}
+	return strings.HasPrefix(s, "http://") || strings.HasPrefix(s, "https://")
+}
+
 // ToConfig 从 config 表重建 *types.Config
 func (r *ConfigRegistry) ToConfig() *types.Config {
 	cfg := &types.Config{}
@@ -817,10 +825,12 @@ func (r *ConfigRegistry) ToConfig() *types.Config {
 	} else {
 		seen := make(map[string]bool)
 		for _, src := range cfg.LLM.Sources {
-			if src.BaseURL != "" && !seen[src.BaseURL] {
-				seen[src.BaseURL] = true
-				cfg.Defaults.LLMEndpoints = append(cfg.Defaults.LLMEndpoints, src.BaseURL)
+			baseURL := strings.TrimSpace(src.BaseURL)
+			if !validLLMEndpoint(baseURL) || seen[baseURL] {
+				continue
 			}
+			seen[baseURL] = true
+			cfg.Defaults.LLMEndpoints = append(cfg.Defaults.LLMEndpoints, baseURL)
 		}
 	}