feat(affiliate): 完善邀请返利系统

- 修复返利不到账的根因：tryClaimAffiliateRebateAudit 中 PostgreSQL 参数类型推断冲突
  - 补全 OAuth 注册路径（LinuxDo/OIDC/WeChat/Pending Flow）的邀请码绑定
  - 前端 OAuth 注册页面传递 aff_code 参数
  - 新增返利冻结期机制：可配置冻结时间，到期后自动解冻（懒解冻）
  - 新增返利有效期：绑定后 N 天内有效，过期不再产生返利
  - 新增单人返利上限：超出上限部分精确截断
  - 增强返利流程 slog 结构化日志，便于排查问题
  - 已邀请用户列表增加返利明细列

backend/migrations/133_affiliate_rebate_freeze.sql

@@ -0,0 +1,17 @@
+-- 1) Add frozen quota column to user_affiliates for rebate freeze period.
+ALTER TABLE user_affiliates
+    ADD COLUMN IF NOT EXISTS aff_frozen_quota DECIMAL(20,8) NOT NULL DEFAULT 0;
+
+COMMENT ON COLUMN user_affiliates.aff_frozen_quota IS 'Rebate quota currently frozen (pending thaw after freeze period)';
+
+-- 2) Add frozen_until column to user_affiliate_ledger for per-entry freeze tracking.
+-- NULL = no freeze (or already thawed); non-NULL = frozen until this timestamp.
+ALTER TABLE user_affiliate_ledger
+    ADD COLUMN IF NOT EXISTS frozen_until TIMESTAMPTZ NULL;
+
+COMMENT ON COLUMN user_affiliate_ledger.frozen_until IS 'Rebate frozen until this time; NULL means already thawed or never frozen';
+
+-- 3) Partial index for efficient thaw queries (only rows still frozen).
+CREATE INDEX IF NOT EXISTS idx_ual_frozen_thaw
+    ON user_affiliate_ledger (user_id, frozen_until)
+    WHERE frozen_until IS NOT NULL;