fix(saas): Phase 5 regression fixes — SQL type casts + test data corrections

- Fix usage_stats SQL: add ::timestamptz cast for Option<String> params
- Fix usage_stats SQL: add ::bigint cast for COALESCE(SUM(...))
- Fix telemetry INSERT: add ::timestamptz cast for reported_at column
- Fix config_analysis_empty test: seed data makes total_items > 0
- Fix key_pool_crud test: key_value must be >= 20 chars
- Fix SkillManifest test helpers: add missing tools field

All 1048 tests pass: 580 Rust + 138 SaaS + 330 Desktop Vitest

crates/zclaw-saas/tests/model_config_test.rs

@@ -229,6 +229,6 @@ async fn usage_stats_empty() {
     let (app, _pool) = build_test_app().await;
     let token = register_token(&app, "usageuser").await;
     let (status, body) = send(&app, get("/api/v1/usage", &token)).await;
-    assert_eq!(status, StatusCode::OK);
+    assert_eq!(status, StatusCode::OK, "usage stats response: {body}");
     assert_eq!(body["total_requests"], 0);
 }