feat(auth): add skip persistence context key for file watcher events

Introduce `WithSkipPersist` to disable persistence during Manager Update/Register calls, preventing write-back loops caused by redundant file writes. Add corresponding tests and integrate with existing file store and conductor logic.

sdk/cliproxy/auth/persist_policy.go

@@ -0,0 +1,24 @@
+package auth
+
+import "context"
+
+type skipPersistContextKey struct{}
+
+// WithSkipPersist returns a derived context that disables persistence for Manager Update/Register calls.
+// It is intended for code paths that are reacting to file watcher events, where the file on disk is
+// already the source of truth and persisting again would create a write-back loop.
+func WithSkipPersist(ctx context.Context) context.Context {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	return context.WithValue(ctx, skipPersistContextKey{}, true)
+}
+
+func shouldSkipPersist(ctx context.Context) bool {
+	if ctx == nil {
+		return false
+	}
+	v := ctx.Value(skipPersistContextKey{})
+	enabled, ok := v.(bool)
+	return ok && enabled
+}