Debounce continuous View controls, and fix review findings from #331

[dovvnloading]

Problem

Five issues found reviewing #331:

1. Continuous controls flooded the wire. The colour pickers and sliders committed on every change event. A native colour picker emits changes continuously while the pointer moves inside it, and each one fired an intent that triggered a full state republish - so choosing a colour, or dragging any slider, put roughly a hundred round trips on the wire. This is the only finding with user-visible impact.
2. Touch and pen could not pan. Redesign the View panel and restore drag speed's real meaning: pan sensitivity #331 disabled React Flow's built-in pan so the speed factor could apply, but bound the replacement to mouse events only. React Flow's own pan was pointer-based, so touch and stylus users lost canvas panning entirely.
3. Dead values in dragStartRef. It held start positions only while the drag-speed factor scaled node motion from its origin. That factor now applies to panning, so nothing read the values - only membership was ever checked.
4. Dead assignment. ConnectionCanvas set a stroke width before its draw loop that every iteration immediately overwrote.
5. The stylesheet contradicted itself. It described the chip class as the multi-select idiom, and Redesign the View panel and restore drag speed's real meaning: pan sensitivity #331 then applied it to the Chat Library's single-select workspace tabs.

Change

• Continuous controls show the in-flight value immediately and commit the last one after a short pause, using the same debounce posture the canvas already uses for viewport reporting. Pending state clears whenever a fresh value arrives with nothing in flight, so a server-side clamp is always what ends up displayed rather than a local value the backend rejected. Discrete controls - presets, grid style, toggles - stay immediate.
• Pan handlers are pointer-based, including pointercancel, and the pane sets touch-action so the browser cannot claim a touch drag for scrolling before the handler sees it.
• dragStartRef is a Set of the ids the gesture is carrying, which is all the drag-stop change needs in order to be recognised.
• The redundant stroke-width assignment is removed.
• The chip class comment now describes what it is actually for: selections drawn from an open-ended, data-driven set, carrying no single/multi-select meaning of its own, as distinct from the segmented control used for short fixed sets of mutually exclusive choices.

Test plan

• Full frontend check passes: schema, types, lint (0 errors), 1928 tests, production build, bundle size
• Two ChartNodeView failures observed during one run were reproduced as pre-existing parallel-load flakiness on a lazily-loaded component - the file passes in isolation and on a repeat full run, and this change touches only a comment in it