Timeline plugin: timeline view

[sandesh-sp]

Replaces the timeline view and layer row placeholders with the d3 implementation: top and bottom time axes, a dashed row per visible layer with its time-range bars, and a draggable scrubber that previews while dragging and commits on release. Scroll zooms and pans; the view hands a reset-zoom callback back to the adapter.

Stack — merge in order, starting from the base:

1. Timeline plugin: shell and component placeholders #239 shell and component placeholders → development
2. Timeline plugin: timeline view #240 timeline view
3. Timeline plugin: date selector #241 date selector
4. Timeline plugin: playback controls #242 playback controls
5. Timeline plugin: time mode control #243 time mode control

[sandesh-sp]

Review pass over the stack (#239–#243). Five issues in this PR, pushed as 9d2d328. Rebased on the fixes in #239.

• The scrubber couldn't be dragged on touch. Both hit targets bound only onMouseDown and the drag loop used window mouse events; the d3-zoom filter additionally rejects touchstart on .timeline-scrubber-handle, so the ±5px band around the current time was inert to touch as well. That matters because TimelineTool explicitly awaits app:isMobile and switches to a width: 'full', height: 300 layout — touch is a supported mode. Moved to Pointer Events with setPointerCapture, which covers mouse, touch and pen in one path and keeps tracking when the pointer leaves the SVG, plus touch-action: none so the browser doesn't take the gesture for a scroll.

• A drag released outside the main SVG swallowed the next click. didDragRef was only cleared by a trailing click on that SVG, and the diamond sits flush against its top edge with a separate <svg> immediately above — drift a few px up while releasing and the flag stayed set, silently dropping the next click-to-seek. Now cleared on pointer up.

• Clicking the handle committed a seek. stopPropagation on mousedown doesn't suppress the later click, and d3's own click suppressor never installs because the zoom filter rejects the handle first. So grabbing the 18px diamond off-centre emitted a time:changeRequested for the time under the cursor — roughly 8h of drift on an 800px/30-day view, from a gesture meant as a no-op. handleTimelineClick now bails when the target is inside .timeline-scrubber-handle.

• Scrubber is keyboard operable. It had no tabIndex, role, aria-value* or key handler. Now role="slider" with min/max/now plus a UTC-formatted aria-valuetext, arrow keys stepping by the current granularity, and Home/End for the range ends.

• Layer tooltips were dead code. .layer-timelines { pointer-events: none } is inherited by every descendant rect, so the <title> elements LayerTimeline renders never surfaced. Re-enabled on .layer-time-range only.

Worth noting what held up under scrutiny: the d3 machinery is solid. Degenerate domains and a zero-width container don't produce NaN (d3-scale's normalize returns constant(0.5)), zoom state survives behavior re-mounting, the wheel listener is correctly non-passive, and svg.on('.zoom', null) removes exactly d3's namespace. No listener or observer leaks.

tsc --noEmit clean, 898 unit tests pass.