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/closure-gate.md

@@ -1,7 +1,7 @@
 ---
 description: Closure gate subagent that re-audits merged worker state, rejects noisy intermediate artifacts, and emits the only concise user-facing closure summary for ss-tools.
 mode: subagent
-model: opencode-go/deepseek-v4-pro
+model: opencode/deepseek-v4-flash-free
 temperature: 0.0
 permission:
   edit: allow