M2.14 Files: show root MMS inventory first; bound COMTRADE enrichment - #593

Field regression addressed

The Browser Files path synchronously awaited a full FaultRecordTransferClient.DiscoverAsync recursive traversal (depth 4 / 128 directories / 20k entries) before requesting or rendering the root MMS FileDirectory. A slow, unsupported or timed-out COMTRADE scan could make an otherwise valid root file listing appear entirely unreadable.

Minimal optimized consumer change

• One ARIEC-backed MMS transfer association remains the only network authority; root FileDirectory is read first and presented to the existing native WPF Browser as soon as returned.
• Reuse Iec61850FaultRecordCatalogBuilder.Build to identify supported root CFG/DAT bundles in-memory without a second root directory scan. If the root has no directory candidates, skip expensive recursive discovery entirely.
• When directory candidates exist or root fails, perform optional recursive fault-record discovery with a 30-second linked budget, retain usable root entries if traversal fails or times out, and surface partial-status diagnostics in a compact tooltip.
• Publication remains device/association/read-operation fenced. Downloads are still gated by the existing verified complete-record catalog; no generic arbitrary-file downloads, no additional client/decoder, no new background polling.
• Deterministic regression covers root-only fast-path, early UI publication order, recursive timeout/failure, root failure fallback, and operator cancellation.

Boundaries and acceptance

BCUGE FileDirectory still requires physical replay. Field-specific nested directories may require a separate tested follow-up; this patch does not promise unlimited traversal or generic file download. Stack on #592, no main, ARIEC engine pin, release or control operation changes. Exact-SHA Windows CI required before approval.