refactor(referral): prune dead code and formalize ops list header

- remove unused AuthReader::invitation_mode and ReferralAttribution
  helpers (get_or_create_code / validate_ref); contract test now
  asserts the canonical invit_code_s reader in CreditsRuntime
- drop legacy aksrt_invite table from uninstall cleanup list
- track referral code creation time (aksrt_referral_code_created)
  and surface it in the referral ops REST list
- formalize ops list headers (归属用户/推广码/启用状态/推广用户数/
  有效付费用户数/创建时间) and right-align count columns

uninstall.php

@@ -30,7 +30,6 @@ $tables = [
     'aksrt_asset_transaction',
     'aksrt_asset_account',
     'aksrt_signin_log',
-    'aksrt_invite',
     'aksrt_dl_token',
     'aksrt_notification',
     'aksrt_report',