# 031 — Timeline start/end markers, cursor hover, and live drag readout

## Summary

`LogTimeline` (`webapp/src/components/LogTimeline.tsx`) shows a bar per
bucket with only a per-bar `title` tooltip on native hover, and a drag
selection that's silent until `handleMouseUp` fires `onSelectRange`. Add
always-visible start/end labels, a hover readout that tracks the cursor, and
a live-updating readout while dragging.

## Scope

- **Start/end markers**: render the sequence index and timestamp of the
  first and last visible bucket at the two ends of the timeline (using
  `domainStart`/`domainEnd`, already computed at
  `LogTimeline.tsx:52-53`), always visible, not hover-only.
- **Cursor hover readout**: on `onMouseMove` (already wired for drag at
  `handleMouseMove`, `LogTimeline.tsx:65`), when not dragging, compute the
  bucket at or immediately before the cursor via `xToMs` and show its
  timestamp/count in a readout near the cursor — replacing reliance on the
  native per-bar `title` attribute (`LogTimeline.tsx:135`).
- **Live drag readout**: while `dragging` is true (`LogTimeline.tsx:78`), show
  the resolved start/end (`xToMs(dragStartX)`/`xToMs(dragCurrentX)`) updating
  on every `handleMouseMove`, not just after `handleMouseUp` resolves the
  final range — the drag rectangle already updates live (`selRect`,
  `LogTimeline.tsx:79-84`); this adds the numeric readout next to it.

## Acceptance criteria

- The timeline always shows the sequence/timestamp of its first and last
  bucket, without needing to hover.
- Moving the mouse over the timeline (not dragging) shows the timestamp/count
  of the bucket under (or just before) the cursor, updating as the mouse
  moves.
- While dragging, the displayed start/end timestamps update continuously as
  the drag extends, matching the already-live selection rectangle.

## Depends on

None — builds on the existing `LogTimeline` drag/hover plumbing.