Event Logs UI phase 4b: Coverage note with Elevate action #831

Part of #823.
Depends on: #830.
Spec: docs/superpowers/specs/2026-10-08-event-logs-workbench-ui-handoff-design.md (see the section references below).
Design: Claude Design canvas "Event Log Viewer Redesign" (board exports to be attached).

Spec: §8.13 (Insights tab item 2), mockup Main

Scope (4 files)

• EvtxCoverageBanner.tsx (+ existing test): rail variant — "{channel} channel not read. Findings may be incomplete."
  with lock icon and "Elevate" action opening the existing RestartAsAdministratorDialog; hidden when elevated or non-Windows.
• EventDiagnosisPanel.tsx: render the note above the coverage disclosure.
• EventLogWorkspace.tsx: remove the banner from above the grid.

Acceptance

• Shown only when an accessDenied gap exists; other gap kinds stay in the coverage disclosure.
• tsc / tests / diff-check / screenshots pass.

Generated by Claude Code