P0-D: live signal viewport layout guard and field-evidence UX hardening

[masarray]

P0-D field-driven UI + data-evidence hardening; stacked on P0-C consumer #627. Exact evidence inspected privately (no customer endpoints or screenshots committed). 38 selected II_PTOC1 FC attributes: 35 OBSERVED, 1 READ_FAILED for an empty Octet64 origin identifier, 2 NOT_OBSERVED_NO_ATTEMPT_EVIDENCE (nameplate swRev and d). Correct a proven zero-byte MMS OCTET STRING into visible Empty OCTET STRING (0 bytes) rather than conflating with failed/no-scalar; never admit empty VisibleString or Unknown raw BER. Add independent positive/negative regression. Live Signal Values grid gets explicit star-row stretch, virtualization and scroll with XML regression. Prior live test: 18/18 report-fed DataSet members; RCB partial catalog continuation and BufOvfl remain unresolved. Neither this PR nor existing P0-A/B/C prove all 4,090 attributes, absolute SOE continuity, cross-DPI screenshots, taskbar identity, independent simulator chaos suite, or release. CI pending; keep draft and no physical promotion.

[masarray]

Superseded without merge: #628 remains the single authoritative typed MMS empty-value / SSOT evidence implementation. The independent Live Signal viewport XAML layout (without duplicate ProjectReadValue logic) is ported into a clean stacked branch in #630. #629 exact HEAD 0f73f184... failed Windows compile at P0DTypedEmptyOctetEvidenceTests.cs:37 (CS8418, using on IAsyncDisposable); simply correcting the compile syntax would still leave conflicting OCTET policies and a namespace-sensitive XML test. #630 keeps only the orthogonal viewport change and corrects regression compatibility. Do not merge or cherry-pick this branch wholesale; pending #630 Windows CI and physical DPI validation.