fix(panels): proportional absorber pins, stale-pin cleanup, double-click to reset

[nishasdk]

What

ResizablePanel reliability fixes

• Switch wrapperRefs from an index-keyed array to an ID-keyed Map — drag measurement now survives dynamic children changes (e.g. the plan tab appearing mid-drag)
• Add flexGrow prop to PanelChild so absorbers can be weighted (notes-files gets a smaller weight, leaving the AI terminal ~2/3 of the remaining space)
• Store absorber pins as flex-grow ratios instead of pixel values so they scale proportionally when the window is resized
• Detect and clear asymmetric absorber pins (one absorber pinned while siblings are not) — these are stale pixel values from before the child was promoted to absorber status, and would otherwise starve the other absorbers

Double-click on tiling resize handles to unpin

• Double-clicking a resize handle between two task columns resets both panels to the default equal split without any dragging

Layout cleanup

• Remove the 40vh max-height from TaskNotesBody — it was a workaround for content-size bubbling up the flex chain; notes-files is now a proper weighted absorber so height is layout-driven, not content-driven

Why

Pinned panels previously stored pixel values, which go stale when the window is resized or when an absorber configuration changes. Storing ratios instead keeps the layout self-healing. The double-click reset gives users a quick escape hatch without needing to drag.

Testing

1. Pin two panels at different widths, then resize the window → proportions should hold
2. Double-click a tiling resize handle → both panels should snap back to an equal split
3. Open the plan tab (which adds a new absorber) → drag should measure correctly with no visual jump
4. No layout breakage in focus mode or with long plan markdown open

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PS. just cosmetic fixes! just wanted to test what submitting a PR on parallel code would look like :)