feat: add group activation command

src/auto-reply/group-activation.ts

@@ -0,0 +1,23 @@
+export type GroupActivationMode = "mention" | "always";
+
+export function normalizeGroupActivation(
+  raw?: string | null,
+): GroupActivationMode | undefined {
+  const value = raw?.trim().toLowerCase();
+  if (value === "mention") return "mention";
+  if (value === "always") return "always";
+  return undefined;
+}
+
+export function parseActivationCommand(raw?: string): {
+  hasCommand: boolean;
+  mode?: GroupActivationMode;
+} {
+  if (!raw) return { hasCommand: false };
+  const trimmed = raw.trim();
+  if (!trimmed) return { hasCommand: false };
+  const match = trimmed.match(/^\/?activation\b(?:\s+([a-zA-Z]+))?/i);
+  if (!match) return { hasCommand: false };
+  const mode = normalizeGroupActivation(match[1]);
+  return { hasCommand: true, mode };
+}