feat(core): resolve declared configuration with env and file precedence

按 显式 env > autoEnable > 配置文件 > default 的优先级链解析每个已声明
key，支持标量 env 填充切片、duration 与结构体切片解码，非法 env 值不再
静默回退而是报 ErrConfigType。

backend/core/extpoints/config.go

@@ -138,12 +138,13 @@ type ConfigExtension interface {
 // ConfigRegistry implements ConfigExtension. Declarations are additive; values are
 // computed once by Resolve and reused by every later read.
 type ConfigRegistry struct {
-	mu      sync.RWMutex
-	src     ConfigSource
-	decls   map[string]*configDecl
-	order   []string
-	values  map[string]any
-	origins map[string]string
+	mu       sync.RWMutex
+	src      ConfigSource
+	decls    map[string]*configDecl
+	order    []string
+	values   map[string]any
+	origins  map[string]string
+	resolved bool
 }
 
 // NewConfigRegistry creates an empty configuration registry. A nil src is allowed so