Fix FAT LIVE VALUE realtime authority and WPF scroll freeze

[masarray]

Scope

Narrow recovery patch on top of the Build #1888 / 712e2c55 FAT line. No FAT layout redesign, no Static DataSet rollback, and no ARIEC61850 engine change.

Root cause found

IoListTestingWindow.LiveValueAuthority.cs changed VirtualizingPanel.VirtualizationMode from a Loaded/dispatcher path. WPF forbids changing that attached property after the ItemsHost has been measured, matching the observed InvalidOperationException and blank/frozen FAT window.

Fix

• Remove all runtime mutation of VirtualizationMode / IsVirtualizing; baseline XAML owns virtualization.
• Keep the authoritative LIVE VALUE cell event-driven.
• Prefer the actual Iec61850MonitorPoint.Value report/poll process image over potentially stale ControlCurrentValue.
• Canonicalize boolean display (false/False/FALSE -> stable False) and skip identical TextBlock.Text assignments to reduce scroll/update flicker.
• Preserve Runtime value only as last-resort display fallback; no evidence/session/acquisition mutation.

Regression guards

Tests assert:

• shared Engineering live source is used;
• live monitor point has precedence over control cache;
• no runtime virtualization mutation is reintroduced;
• boolean text is canonicalized and redundant paints are skipped;
• Value 1 / Value 2 evidence and acquisition policy remain untouched.

Physical relay bench validation is still required before merging into a release line.

[masarray]

Superseded by clean recovery PR #260. The implementation remains reference material only; its ancestry contains earlier recovery commits and it will not be used as the final baseline. Do not merge.