The vertical toolbar's shape button is now a compound slot driven by
`Document.ui.shape_tool` (defaults to Rect). Click it to open a
`ShapePicker` dropdown anchored immediately to the right of the
slot — seven rows mirror the TS app's shape-tool-dropdown:
· Rectangle (Square icon)
· Ellipse (Circle)
· Polygon (Triangle)
· Line (Minus)
· Icon (Sparkles, opens icon picker — host follow-up)
· Import Image or SVG… (ImagePlus, opens file dialog — host follow-up)
· Pen (PenTool)
Picking a shape updates ui.shape_tool (so the toolbar slot's icon
flips), sets doc.tool to that variant, and closes the panel. Click
anywhere else closes silently.
* New Tool variants: Ellipse / Polygon / Line / Pen. Tool::is_shape()
reports membership in the slot's group so the slot highlights when
any of them is active.
* New icons: Circle, Triangle, PenTool, ImagePlus (lucide d-strings).
* New widget shape_picker.rs (≤ 280 lines) with hit-test + Widget
impl + 3 unit tests; ShapeChoice variant for the host to dispatch
on (Tool / OpenIconPicker / ImportImageOrSvg).
* PropertyLabels-style locale lookup falls back to English literals
for the row labels (shapes.rectangle / ellipse / polygon / line /
icon / importImageSvg / pen) — already present in zh.ts.
* Native host wires the open/close/dispatch loop alongside the
existing locale picker; paint slot z-priority sits below the
locale picker so a stack of overlays still does the right thing.
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