perf: visibility-gate dashboard render loop

Co-authored-by: PR0M3TH3AN <[email protected]>

src/test_logs/TEST_LOG_2026-02-16.md

@@ -0,0 +1,13 @@
+# TEST LOG: perf-agent (2026-02-16)
+
+## Verification Steps
+
+1. **Static Analysis**: Verify `dashboard/index.html` contains `document.hidden` check inside `setInterval`.
+2. **Static Analysis**: Verify `dashboard/index.html` contains `document.addEventListener('visibilitychange', ...)` handler.
+3. **Linting**: Run `npm run lint` to ensure no syntax errors or style violations.
+
+## Results
+
+- [x] Static Analysis (Hidden Check): Passed (Verified in `dashboard/index.html`)
+- [x] Static Analysis (Visibility Listener): Passed (Verified in `dashboard/index.html`)
+- [ ] Linting: Scheduled for Scheduler Completion step.