feat(ui): virtualized event timeline

[sepehr-safari]

Summary

The inspector's centerpiece: a virtualized event timeline. One row per OCPP
event, in a model-owned split beside a detail pane — and it stays viewport-sized
in widget nodes no matter how large the trace is.

• Windowed virtual list (ui.virtualList / ui.virtualWindow) over the
  active trace's events. The runtime owns the scroll; the view builds only the
  visible window, keyed by event index. A 500 000-event trace materializes a few
  dozen row nodes, not 500k — well under the 1024 widget-node per-view budget.
• Rows: a severity dot (shown when the event participates in a detected
  failure, colored by severity), the index, UTC time-of-day, a direction
  affordance (CS→CSMS / CSMS→CS / unknown), the message (action for calls, the
  responded UniqueId for results, code: description for errors), and the message
  type. Clicking a row selects the event.
• Split layout: the timeline (left) and a detail pane (right) sit in a
  model-owned split; the divider fraction echoes back through value after
  each drag (timeline_resized).
• Detail pane (first cut): the selected event's normalized fields. The full
  inspector — raw OCPP-J array, payload tree, and session panel — is feat(ui): message inspector + session panel #30; this
  establishes the pane and the selection wiring.

Verification

• native test -Dplatform=null — 65/65 pass (macOS; CI also runs Linux).
  New coverage: the timeline renders sample rows; a row press selects the event
  and the detail pane reflects it (through msgForPointer); the splitter fraction
  round-trips; the virtual window stays viewport-sized at 500 000 items
  (window.itemCount() < 64); and the accessibility sweep still passes over the
  split + timeline tree.
• native check --strict clean; native build produces the ReleaseFast binary.
• scripts/smoke.sh now also asserts a timeline row (BootNotification) renders
  live — the CI Linux · Xvfb job drives the real window.

Notes

• The 500k-event end-to-end capacity claim (a real 100 MB trace parsed and
  correlated) lands with the trusted-ingestion engine path in feat(engine): trusted-ingestion parse path + streaming (500k / 100 MB) #29; this PR proves
  the UI side — the window math is viewport-bounded regardless of item count.
• Direction and severity are drawn with built-in vector icons carrying
  accessibility labels (no font-coverage risk, a11y-clean).

Closes #28