Deprecate legacy Login/Register, add admin events, members, webhooks

- Mark Register() and Login() as Deprecated (use Better Auth directly)
- Add admin_events.go, members.go, webhooks.go to match backend API
- Sync types with backend changes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

admin_events.go

@@ -0,0 +1,17 @@
+package elydora
+
+import "fmt"
+
+// ListAdminEvents retrieves recent administrative events for the organization.
+// An optional limit (1–100) may be provided; pass 0 to use the server default (20).
+func (c *Client) ListAdminEvents(limit int) (*ListAdminEventsResponse, error) {
+	path := "/v1/admin/events"
+	if limit > 0 {
+		path = fmt.Sprintf("%s?limit=%d", path, limit)
+	}
+	var result ListAdminEventsResponse
+	if err := c.doGet(path, &result); err != nil {
+		return nil, err
+	}
+	return &result, nil
+}