Fix subvariation display, progress bar, and linked-instrument discard

- ast-parser: read for_value= prop for sub-variations (was always null,
  causing fallback to positional "subvariation N" label)
- StatusPoller: calculate progress from currently_rendered_notes /
  notes_in_total; show remaining_time string from status.json
- ShapeEditor/EnvelopeEditor: pass { undo } through onChange so callers
  can revert in-place mutations
- PaneFO: makeChangeHandler stashes undo from info arg; discardEdit
  calls undo() before clearing pendingEdit; depends_on handler provides
  its own undo for the inline node.dependsOn mutation

static/components/ShapeEditor.js

@@ -1,7 +1,8 @@
 import { h } from 'vue';
 
 // Renders a shape's coord table with cascade-shift and an SVG preview.
-// `shape` is mutated in place; `onChange` called after each mutation.
+// `shape` is mutated in place; `onChange` called after each mutation with
+// { undo } so callers can revert if needed.
 
 export const ShapeEditor = {
     props: ['shape', 'onChange'],
@@ -14,27 +15,31 @@ export const ShapeEditor = {
             const delta = num - old;
             coord[field] = num;
 
-            // cascade-shift: if x increased past next coord, shift all following
+            const shifted = [];
             if (field === 'x' && delta > 0) {
                 for (let j = i + 1; j < props.shape.coords.length; j++) {
                     if (props.shape.coords[j].x <= num) {
+                        shifted.push({ j, ox: props.shape.coords[j].x });
                         props.shape.coords[j].x += delta;
                     } else break;
                 }
             }
-            props.onChange?.();
+            props.onChange?.({ undo: () => {
+                coord[field] = old;
+                for (const { j, ox } of shifted) props.shape.coords[j].x = ox;
+            }});
         }
 
         function addCoord() {
             const coords = props.shape.coords;
             const lastX = coords.length ? coords[coords.length - 1].x + 1 : 1;
             coords.push({ x: lastX, y: 0, z: 1, isSharp: false });
-            props.onChange?.();
+            props.onChange?.({ undo: () => coords.pop() });
         }
 
         function removeCoord(i) {
-            props.shape.coords.splice(i, 1);
-            props.onChange?.();
+            const removed = props.shape.coords.splice(i, 1)[0];
+            props.onChange?.({ undo: () => props.shape.coords.splice(i, 0, removed) });
         }
 
         function renderSvg() {
@@ -55,19 +60,14 @@ export const ShapeEditor = {
                 return [sx, sy];
             };
 
-            const points = coords.map(c => toSvg(c).join(',') ).join(' ');
+            const points = coords.map(c => toSvg(c).join(',')).join(' ');
 
             return h('svg', {
                 class: 'se-shape-svg',
                 viewBox: `0 0 ${W} ${H}`,
                 preserveAspectRatio: 'none',
             }, [
-                h('polyline', {
-                    points,
-                    fill: 'none',
-                    stroke: '#2a6aaa',
-                    'stroke-width': '1.5',
-                }),
+                h('polyline', { points, fill: 'none', stroke: '#2a6aaa', 'stroke-width': '1.5' }),
                 ...coords.map(c => {
                     const [sx, sy] = toSvg(c);
                     return h('circle', { cx: sx, cy: sy, r: 2.5, fill: '#6aacff' });
@@ -101,7 +101,11 @@ export const ShapeEditor = {
                             })),
                             h('td', null, h('input', {
                                 type: 'checkbox', checked: !!coord.isSharp,
-                                onChange: e => { coord.isSharp = e.target.checked; props.onChange?.(); },
+                                onChange: e => {
+                                    const old = coord.isSharp;
+                                    coord.isSharp = e.target.checked;
+                                    props.onChange?.({ undo: () => { coord.isSharp = old; } });
+                                },
                             })),
                             h('td', null, h('button', { onClick: () => removeCoord(i) }, '✕')),
                         ])