test(saas): Phase 1 integration tests — billing + scheduled_task + knowledge (68 tests)

- Fix TIMESTAMPTZ decode errors: add ::TEXT cast to all SELECT queries
  where Row structs use String for TIMESTAMPTZ columns (~22 locations)
- Fix Axum 0.7 route params: {id} → :id in billing/knowledge/scheduled_task routes
- Fix JSONB bind: scheduled_task INSERT uses ::jsonb cast for input_payload
- Add billing_test.rs (14 tests): plans, subscription, usage, payments, invoices
- Add scheduled_task_test.rs (12 tests): CRUD, validation, isolation
- Add knowledge_test.rs (20 tests): categories, items, versions, search, analytics, permissions
- Fix auth test regression: 6 tests were failing due to TIMESTAMPTZ type mismatch

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/zclaw-saas/src/workers/cleanup_refresh_tokens.rs

@@ -20,7 +20,7 @@ impl Worker for CleanupRefreshTokensWorker {
     }
 
     async fn perform(&self, db: &PgPool, _args: Self::Args) -> SaasResult<()> {
-        let now = chrono::Utc::now().to_rfc3339();
+        let now = chrono::Utc::now();
         let result = sqlx::query(
             "DELETE FROM refresh_tokens WHERE expires_at < $1 OR used_at IS NOT NULL"
         )

crates/zclaw-saas/src/workers/log_operation.rs

@@ -27,7 +27,7 @@ impl Worker for LogOperationWorker {
     }
 
     async fn perform(&self, db: &PgPool, args: Self::Args) -> SaasResult<()> {
-        let now = chrono::Utc::now().to_rfc3339();
+        let now = chrono::Utc::now();
         sqlx::query(
             "INSERT INTO operation_logs (account_id, action, target_type, target_id, details, ip_address, created_at)
              VALUES ($1, $2, $3, $4, $5, $6, $7)"

crates/zclaw-saas/src/workers/record_usage.rs

@@ -29,7 +29,7 @@ impl Worker for RecordUsageWorker {
     }
 
     async fn perform(&self, db: &PgPool, args: Self::Args) -> SaasResult<()> {
-        let now = chrono::Utc::now().to_rfc3339();
+        let now = chrono::Utc::now();
         sqlx::query(
             "INSERT INTO usage_records (account_id, provider_id, model_id, input_tokens, output_tokens, latency_ms, status, error_message, created_at)
              VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)"

crates/zclaw-saas/src/workers/update_last_used.rs

@@ -23,7 +23,7 @@ impl Worker for UpdateLastUsedWorker {
     }
 
     async fn perform(&self, db: &PgPool, args: Self::Args) -> SaasResult<()> {
-        let now = chrono::Utc::now().to_rfc3339();
+        let now = chrono::Utc::now();
         sqlx::query("UPDATE api_tokens SET last_used_at = $1 WHERE token_hash = $2")
             .bind(&now)
             .bind(&args.token_hash)