Player pane height is computed once and never adapts to the window

[vishnuv688]

Not mobile-specific — it is wrong for every trace, just least visible on a desktop one.

packages/app/src/components/workbench.ts has no resize handling at all: no connectedCallback, no listener. The player pane's height comes from a DragController whose initialPosition is a pixel number computed once, at construction, from whatever window was open at the time. Nothing ever recomputes it.

Measured by opening a trace in a small window and then resizing:

window	pane height	phone rendered
1280x720	124px	13x28
1600x1000	124px	13x28
2560x1440	124px	13x28

A 13px-wide capture on a 2560px screen. The snapshot component was faithfully filling the box it was given; the box never changed.

Two parts to a fix:

1. Derive the default pane height from the window as it is now, and re-render on resize. A height the user has dragged is stored and must keep winning.
2. The snapshot component listens for resize and window-drag, so re-fitting depends on whoever changed the layout remembering to announce it. A ResizeObserver on its own box covers every case, including those that fire no event (dock divider, sidebar collapse, browser zoom).