fix(health): suppress 404 when health monitor disabled + fix audit test assertion

- Sidebar.svelte: defer healthStore.refresh() until feature flags confirm
  health_monitor is enabled; skip entirely when disabled
- health.js: remove throw error from catch block — log and return null
  instead, preventing 'Uncaught (in promise)' on expected 404
- test_report_audit_immutability.py: fix mock assertions —
  audit_service uses logger.reason/reflect/explore, not logger.info
- HealthStore and Sidebar now produce zero network noise when
  FEATURES__HEALTH_MONITOR=false

.opencode/agents/qa-tester.md

@@ -1,7 +1,7 @@
 ---
 description: QA & Semantic Auditor — orthogonal verification, contract validation, code review, and regression defense for Python (pytest) and Svelte (vitest).
 mode: all
-model: opencode-go/kimi-k2.6
+model: opencode-go/qwen3.6-plus
 temperature: 0.1
 permission:
   edit: allow