Stack controls under sequencer and enable slider drag

[jeromepotter]

Motivation

• Prevent side panels and planet chips from overlapping the main sequencer by stacking NOTES, GATES and ORBS under the circle and positioning chips relative to the orbit radius.
• Restore usable touch dragging for all range controls while keeping the existing pill-style filled visual for sliders.

Description

• Reflowed UI: moved NOTES, GATES and the ORBS button into a centered #side-controls stack and positioned #planet-list-wrap below the sequencer using orbit-based layout in updateSidePanelsForViewport().
• Slider & visuals: restored actual range thumb targets and track behavior and added a slider-pill visual wrapper plus CSS for thumb/runnable-track and --slider-fill handling; disabled touch panning with touch-action: none so ranges are draggable on touch.
• Slider helpers & sync: added formatSliderValue(), updateSliderValue(), updateSliderFill() and refreshSliderDisplays() and wired dataset attributes to keep text labels and pill fills synchronized.
• UI behavior & extras: added #modal-overlay for settings click-away dismissal, anchored the global settings panel near the settings button, improved open/resize logic to only toggle panel open state on layout changes, and added undo/redo support (redoStack, redoLastMove, and updated buttons).

Testing

• Started a static server with python -m http.server 8000 and ran a Playwright script to capture desktop and mobile screenshots, which completed and produced artifacts (les-cercles-ui-stacked-desktop.png and les-cercles-ui-stacked-mobile.png) successfully.
• Additional Playwright runs were executed to verify layout variants and produced screenshots (les-cercles-ui-final-*.png and les-cercles-ui-stacked-*.png) without errors; no unit tests were run.

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Codex Task

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