PaneCP article label + PaneFO editable property rows

Article entries in the CP path list now show the article label
(letter/extension) instead of just "article", with a property count
in the meta column. In the FO pane, each property is rendered as an
editable row: key input, value input (coerced via ast-parser.coerce),
scope toggle, morphing default/overwrite label, and per-row remove
button. A "+ add property" button appends a blank defaults entry.
Every edit marks the score dirty.

`coerce` is now exported from ast-parser.js so the FO pane can apply
the same type-inference rules to user input as the parser does to
AST values.

static/components/PaneCP.js

@@ -34,6 +34,10 @@ function shortView(node) {
             return { typeTag: 'motif', label: node.label, meta: node.isStatic ? [{ key: 'static', value: '✓' }] : [] };
         case 'stem_note':
             return { typeTag: 'stem_note', label: String(node.pitch), meta: [] };
+        case 'article': {
+            const n = node.properties?.length ?? 0;
+            return { typeTag: 'article', label: node.name, meta: n ? [{ key: 'props', value: n }] : [] };
+        }
         default:
             return { typeTag: node.type, label: node.type, meta: [] };
     }